Uninstall Windows Vista by putting in the disc for another operating system, booting the computer from the disk and following the instructions to delete the old Windows Vista partition. Make sure to use a full-blown version of the new operating system, and not an upgrade disc, with advice from a network engineer and IT specialist in this free video on Microsoft Windows Vista.
Can't really uninstall Vista like you would a software program inside of Windows. Vista is an operating system, so to get rid of Vista you have to treat it that way. You have to go outside of Vista and then delete what's called the partition that it's installed on and then reformat it with whatever operating system that you'd like, Linux, Windows XP, whatever. So to do that, you would take the disc, whatever operating system you want, let's say in this case XP, which is probably what you're going after if you have Vista, and you take the disc, you'll pop it in, you don't even have to do anything inside of Vista. What I want you to keep in mind though is that you're going to lose all the information that's on the Vista partition, so you want to make sure you back up your pictures, your movies and things like that. So once you have the disc in, you want to pop it in, make sure your computer boots from the CD. It'll ask you to boot from the CD or press any key to boot from the CD. Once that pulls you into the Windows XP set up, once you're there, there will be an option to delete partition. I believe D and then F3 will confirm that you're deleting partition there. Once you have that partition deleted, you then just hit enter and it will install Windows on, or Windows XP on the partition you just deleted. When you come back up, when you re-start your computer back up, it will step you through the Windows set up, setting time zones and things like that, but once that's completed, you'll then have Windows XP instead of Vista. You want to make sure that you also have a full blown version of XP and not an upgrade disc because the upgrade disc won't help you any when you try to install from it. Also make sure you have a legitimate copy because that's, you don't want to pirate or risk incurring Microsoft's wrath.