You don't need to reformat, but I strongly recommend you to NOT install WinXP over your actual WinXP.
If your HDD is "FAT32", then boot with a Win98/WinME diskette and rename your actual Windows directory. Then, reinstall Windows XP on your system in a new directory, after everything is done you will be able to delete your old Windows and a "fresh" system without any format!
I can suggest you that having 2 partitions (split your HDD in 2 logical part) is always a good thing when it comes to system upgrade or reinstalling, you basically have 1 partition for Windows that you can wipe at anytime and a second partition for your programs, games and documents that you don't need to format when you do major OS upgrade, etc...
So, my recommandation for you is to backup your stuff on CD or DVD. Then partition your HDD (a partition of 10Gig is more than enough for Windows XP, the rest for your files, programs, etc...). Then install windows and you will never have any problem in the future.
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You can try to go into your hardware manager i n WinXP and remove all the stuff that is in it related to your motherboard and CPU, then shut down your PC, swap your hardware and reboot your "new system" and have your WinXP CD ready. This might work... But, this can mess everything too!!!
I've had no problems at all performing a "repair" installation when making major hardware changes.
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The problem with having all your app and games on a seperate partition, and re-installing your OS is that a lot, if not all, of you applications/games won't function properly because of missing registry keys.
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On my son's rebuild. I'd hoped to keep the old programs on there by doing a "repair" installation. Didn't work. It just kept rebooting and reloading and reloading. The repair would get to a certain point in the XP Professional installation and then hang. Finally had to do a clean install.
Kinda glad I did.
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I just went from nforce2 to nforce3 250. I have also changed from one nforce board to another.
What I did, was to go into control panel, then device manager. In device manager, I deleted all the drivers that related to my mobo. Then I shut down, and changed mobos. XP even loaded most of the new drivers, without incident. I upgraded them all anyhow.
I know it, but at least, you don't need to wipe everything and you don't lost your save games, documents, etc... by mistake.
I personaly have 2 HDD (my main HDD is partionned). It's the most reliable solution, I often backup to the second HDD and also on a DVD-RAM. And when I need to reinstall Windows for major hardware change, I only have to wipe my Windows partition and I have no worries because I know that all my important data is not on this partition.
By the way, another good trick is to move the default folders from the Windows partition.
"C:\My Documents" becomes "<b>D</b>:\My Documents"
So basically you end up with a C drive that is only containing the Windows folder.