Bootcamp is essentiale a driver package for windows on the mac.
More info on that:
http://www.apple.com/support/bootcamp/
So to be clear, you have to instal this once you are booted into windows xp. ( Keep 'alt' pressed at boot-up, select windows drive)
bootcamp 3.0 you will find on your snow leopard disc.
bootcamp 3.1 :
for windows 32 bit:
http://support.apple.com/kb/DL996?viewlocale=en_US
for windows 64 bit:
http://support.apple.com/kb/DL979?viewlocale=en_US
Once your done, you'll probably have to change your bootdrive to macintosh again. You can change this under systempreferences on the mac side, under startvolume, or bootdisk, or... (something like that, I use a Dutch, or sometimes a German version, but never an English one.)
I don't know if windows xp 64 bit is fully supported though. I thought I read here somewhere that it isn't. Good luck!
One more thing, I hope you formated the windows partition to NTFS instead of FAT32. YOU SHOULD!
I'm going to bed now,(one a.m. here), please let me know how it worked out and I will help you in the morning if it didn't!