I'm not exactly sure what going on here. so let me get this strait:
You buy vista, You buy a new computer. You install vista, and you install Vista drivers. You install XP, but nothing works because you have vista drivers, not xp ones.
now your asking if you can get new drivers for xp without loosing the old ones/reformatting?
um, k. You should probably just be able to download and install the xp compatible drivers. simple as that. Go to the manufacturers site, search your product, and download the XP compatible drivers. You CANNOT use Vista drivers in a XP machine if thats what you wanted to know. Now, if you have a huge hard drive (well, it doesn't have to be that huge) you could partition your HD and do a dual boot setup, where you have a choice to boot either Vista or XP, but it looks like you've done to much damage for that to be an option now. anyways, heres a good link if you'd like to look into it.
http://lifehacker.com/software/top/wind ... 179906.php
anything else you need can be found on google
Not sure if I answered you question, so if I didn't, just ask again.