Well, if you're looking to have a pre-built system instead of building your own, I'd have to say that either brand will work. Since it is a gaming computer, I would suggest at least a 1GHz machine, preferably 1.2GHz, if you have the cash. A 30GB 7200RPM hard drive, 256MB RAM, and a GeForce2 GTS, Pro, Ultra, or if you have the cash, a GeForce3. As to who builds it, Alienware would be your best bet. They are a little pricey, but they patch your machine for you before it goes out the door, so it should be working perfectly. Plus, they do both Intel and AMD chips. I would stay away from the P4 for right now, as it isn't quite what it should be. In Sept/Oct, it should be the best chip around, but if you don't want to wait, go with a P3 or TBird. Also, if you get a TBird, make sure that it is the 266MHz FSB version, and not the 200MHz. It will cost you about $10 more, but your games will thank you.
-SammyBoy
Without Evil, there can be no Good. Therefore, without an Intel, there can be no AMD.