If you go for AMD, don't get anything less than a 2400 chip.

As for p4... Not sure. The only p4 I've had a lot of experience with is my dad's shuttle system. He's got a 2.8 in there. But it's hard to gauge the performance since he uses the onboard video. It lags when I load Diablo2, but I'm sure that's only the fault of the video chip.

The debate rages forever on amd vs. intel, but really they're both good and will do what you want em to pretty well. sometimes one can outperform the other and vice versa. but they're both equally good.

As for good deals I can only suggest what's been suggested. newegg or fry's (outpost.com) or pricewatch.