I already have a windows xp sp3 pro partition. It is NFTS formatted. What will happen to it if I upgrade to snow leopard? I think it won't harm it but I'm not sure so can someone help?
It'll be fine, SL doesn't touch the Boot Camp partition until you manually start the install of the new drivers from the DVD.
If you are really concerned now would be a particularly good time to backup/clone your NTFS partition. (It's always a good time to back things up!) If you have enough disk space, just use Winclone http://www.twocanoes.com/winclone/