if you can keep the same mobo, then I'd go for the P4. Otherwise, if you're buying a new mobo, I'd grab an A64 in a heartbeat. A 2800+ is decent (it often outperforms a P4 3.0GHz, in fact), and if you want to keep your existing mobo and aren't looking to upgrade on the same platform, then that's the way to go. However, if you are looking for a future upgrade, then a $140 socket 939 3000+ and a $90 mobo are a much better investment. (and that's $230, not $300, only about $20-30 more than a comparable P42.8/2800+ + mobo). In fact, 939 mobos will support dual cores, too, so you can keep it for a while. Of course, since you already have a 6600GT AGP, you can't get a PCIe mobo, which is part of the appeal of 939.