How to Rebuild your Computer and Reinstall Windows from Scratch

If you are planning to rebuild a ’slow’ computer by reinstalling
Windows (XP or Vista) from scratch, here’s a pre-installation checklist
+ some time saving tips. You existing data on the Windows PC will not
be affected even if you do a clean install instead of repair or upgrade.
Fix Problems by Reinstalling Windows


As a tech blogger, part of my job involves reviewing software which
is so interesting but frequent installation (followed by
un-installation) of software programs also tend to slow down the
computer.
To deal with this problem, I did a clean installation of Windows
last weekend and re-installed all the important software programs from
scratch. As expected, the boot-up time has reduced and the computer’s
performance has improved significantly. Luckily, this task is not as
complex as it may sound but here are a few things you should remember
before taking the plunge:
Pre-Installation Checklist


1. Get Magical Jelly
to retrieve a list of product keys that were used to install Windows
and Microsoft Office on your computer. Print this information. (Also
see: Determining Windows version)
2. Get Belarc Advisor to create a detailed report of all software programs, hotfixes and hardware devices available in your system. Print this report as well.
3. Uninstall all software programs that had to be activated at the
time of installation (e.g. Adobe Creative Suite, Dragon Naturally
Speaking or Microsoft Office). It’s important that you do a proper
un-installation of these programs through Add/Remove Programs because
simply deleting the folder from Program Files directory will not free
up the license on the manufacturer’s activation server.
4. Install Driver Max to
create a backup of all device drivers currently installed on your
system. This will come handy after reinstallation incase you are not
able to locate the driver installers on the vendor’s website.
5. Create a backup folder on c: (say c:\old_files) and add the following files to this folder
i. Your Outlook pst file that has all the mails, contacts, tasks and other Outlook items.
ii. If you have purchased any custom fonts, copy the relevant ttf files
from the c:\windows\fonts folder. c. All documents, Live Writer drafts,
pictures, music and videos from your My Document folder.
iii. Backup your custom dictionaries from Firefox, Microsoft Word, Live Writer, etc.
iv. Export all browser bookmarks and copy them to the backup folder.
v. Open your Firefox add-ons window, take a screenshot and paste that
image in the backup folder. This is a good way to remember your
favorite Firefox extensions.
vi. Export your podcast subscriptions in iTunes as as OPML (XML) file.
vii. Product keys (serial numbers) of all licensed software.
6. If you have a partitioned hard drive (say C: and D:), just copy*
the backup folder created in step 5 to the D: drive. If you don’t have
a partitioned hard disk or if the size of partition is small, install Live Mesh,
add c:\old_files folder to your Live Mesh account and wait until all
the files are uploaded on to the web. Mesh offers 5 GB of space and it
may therefore be a good idea to burn all the heavy files (like videos,
music, etc) onto a DVD instead of transferring them online.
*You can copy large folders across drives through Windows Explorer or the xcopy utility.
Re-Install Windows from Scratch


Now is the time to do a clean installation of Windows. This is
probably the easiest part. You can either boot your computer from the
original Windows installation CD** or, while you are running Windows,
pop-in the installation CD and run the setup.exe program just like you
would install any other Windows app. Always choose “Fresh Installation”
instead of “Repair”.
**If you installation media doesn’t include the latest service
packs, try creating one yourself. Windows XP with SP3 is available as a
downloadable ISO while you can slipstream SP1 into Vista fairly easily.
Post-Installation Tips


It can take around 30 minutes (or more) for the whole installation to finish. Now jump to the Windows Update
website and let your browser download all the hotfixes, security
updates, driver updates, etc. If your computer is unable to connect to
the Internet, chances are that your computer doesn’t have the proper
network drivers. No problem as you can easily get the drivers from the
dump that you created using DriverMax utility.
If your display is acting funny or there’s no audio, just install
the right drivers from the vendor’s website (preferred approach) or use
your backup media. Once all the patches are installed, Windows Vista
users can free up few gigabytes of disk space by making SP1 permanent. Windows XP users may skip this step.
Now turn on the Firewall and install all the other software programs
and associated updates in any order. The next important step is to clone your disk image via DriveImage XML (free software), Acronis True Image or Norton Ghost.
Windows Vista Ultimate also comes with a “Backup & Restore Center”
that you may use to create a complete backup image of your entire
computer to another drive, external disk or a DVD.
These disk images will come very handy after few months when your
Windows PC get slow again. You won’t have to repeat the rebuilding
exercise as the PC can be easily restored to the original state through
these disk images.
Don’t experiment on your main PC


If you are tech enthusiast who loves to try new software / browser
add-ons, I would strongly recommend that you don’t install these
software on your main system - instead get Virtual PC (it’s free), create a Windows XP / Windows Vista virtual machine and use that environment as your new playground.
Another recommendation - do get a cane of compressed air to remove
all the dirt from components inside the computer case. Sometimes
software may not be the reason behind your slow and slugging PC - the
culprit could be the dust sticking on the CPU heat sink.

Cited from DigitalInspiration

This actually seems a bunch of trouble to go through IMO. I just "down" graded my mom's laptop from Vista to XP and the only things I concerned myself with were:

A: drivers - most important thing to know before attempting to downgrade a PC from Vista back to XP is if there are XP compatible drivers for the machine's hardware. If you cannot find XP compatible drivers for any part of your laptop, you should STOP immediately. PC users have a better chance to downgrade OS than the laptop users do since any component can be easily replaced if its parts are not XP compatible.

B: Windows XP install disc - we had one left over from when they used to ship these things with a new computer. it pays to hold on to those things.

C: Windows install key - it turned out not to be necessary with the disc we used, but a lot of discs will need a windows install key. If you have a Dell computer, they print the install key on the side of the machine rather than printing it on the cd sleve. other manufacturers may do this differently.

D: Backing up data - there wasnt much on this machine data wise since everything was already stored to the network server (in this case it was the Dell PC whose XP install disc we used). If you have a network you can backup your data to another machine temporarily. If no network is present, you can use any kind of media to backup your data - CD/DVD, flash drive, external hard drive - second hard drive if present. You name it.

E: Installation discs for software - obviously when you downgrade an operating system you will be formatting the hard drive to remove the old one and will need to reinstall everything.

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now... it seems this fellow here in this write up is talking about fixing "slowdowns" on a machine which has had the OS installed for a long time and has done lots of program install/uninstalls. It would not hurt to mention that good maintenance can prevent this.

A: run defragmentation occassionally - after installing/uninstalling new softaware and/or copying/deleting lots of files.

B: clean out temporary files often

C: run registry cleaner often - computers that have been used for years will suffer great slowdowns from an overstuffed registry (this happens when people install/uninstall a lot of stuff). Keep it clean of dead links.

D. keep the list of auto-run programs to a minimum - things running automatically at startup will slow the machine down. keep it limited to security and hardware related programs only.

Lots of times when you install an application, it will ask you if you want it to run automatically at startup. That option is usually checked by default, but if you run through the install screens without reading them - you will not notice it. Take your time when installing new software to notice if this question is presented. It will not keep you from starting a program manually if you deselect this option. It WILL save you time on boot-up as well as working memory. Too many auto-start applications is bad for performance not only at start-up but also because they sit in memory - forcing your actual active work to eventually end up in the paging file space, which operates much slower. Sometimes though an application will automatically ad itself to the auto-start list without your permission. Its a bad practice by application developers to do this, but it happens. fortunately there are ways to fix this as I will present a couple methods below for that.
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maintenance appliacations:

A: CCleaner - this application can be used for cleaning out the temporary files that clutter your hard drive, cleaning the registry, and for uninstalling applications

B: Autoruns - this application can be used to maintain the list of auto-starting processes and applications. To keep an application from starting automatically, uncheck the box. (directions in more detail on the website)
-- an alternate method, though not as thorough is to go to start -> run -> type "msconfig" (w/o quotes) and press enter. Go to the "startup" tab and uncheck those applications you do not want to automatically start.
-- other applications that startup automatically will be stored in the start menu -> all programs -> startup folder.

for the maintenance application i prefer to Tuneup Utilities

not tried it to be honest.. I dont know about these so called "speed up your machine" applications. they seem to me to be a waste of money in my opinion. it may be cool for some people but I prefer not to use them.