While helping a friend uninstall Vista so that he could go back to his friendly XP Sp2 that knew his hardware... came across this link which saved me a ton of work
For the uninitiated, Vista needs around 6 Gigs of space to sit down.. yeah you read that right!
Installs quick. Machine starts and shuts down quicker. (But then we didn't have any applications installed) - It didn't recognize the sound card. This lead to same problem with Linux in that you need hardware that plays along with your OS instead of the other way around.
Nothing great, can't hear music, videos needed codecs and didn't play, the default theme looked lik KDE revamped.
Soon enough, uninstalling meant formatting a 10Gig partition and installing XP all over again. I was worried that it may not allow XP again stating something like 'you have a newer version of the OS installed already'
Did a smart thing.. asked Google. Sure enough Google saves the day. http://www.istartedsomething.com/20060622/installing-and-uninstall-vista-beta-2-for-dual-boot-with-xp/
Seems MS has made this easy ( a thumbs up for MS !)
Note: We had a dual boot scenario (XP n Vista)- I don't know if this works for an upgrade.
Ans: Type in “e:\boot\bootsect.exe /nt52 ALL /force” (without quotes, and replacing e: with the drive letter of your Vista DVD).
What this does is rollback your boot loader to its previous state. After that, restart and you should see the familiar XP startup screen. Format the Vista partition and you have your space back. Hurrah !!!