do you have to use windows xp 64 bit to use some of the graphics cards out there like the nvidia geforce 8800 gts ?

No, the bottom line is always make sure that your graphics card is compatible with motherboard.

NO, but you need Vista if you want DX10 support for these new cards.

You just made life easier by asking the geeks here. If you need info on graphics cards, ask the gamers, NOT the PC technicians.

no, just a pci express slot, a good power supply, and the latest drivers from nvidia.