Ulimate Gaming Machine

I am wanting to build a awesome Gaming computer. I have bought some items for it.
1 TB Western Digital 7200 RPM 32 MB cache
1 4850 Diamond Graphic w/ after market cooler (DuOrb)
6 GB og DDR2 PC6400 Dual Channel
Temptiest Case
Ulimate Vista x64 SP1

Left to buy:
I want to buy 850 WATT PSU
Either Intel or AMD Processor

I need help to decide which CPU i should go with for gaming and Internet Browsing?