I agree with the suggestion to build your own PC. It's very easy nowadays (pretty much just plug everything into the power source, turn on the PC and if it doesn't work double check the connections). Think of it this way: building your own rig will give you the same performance, for less $, with a better understanding of how your system works. It really is a smart move to at least consider building your own PC.
However, I would stay away from AMDs in general (personal preference). I previously owned this rig:
AMD 64 X2 6000+
Foxconn 590i SLi board
8800GT
2GB 1066MHz DDR2 RAM
And my current rig performs better:
Intel C2D E6600
ASUS P5B Deluxe
8800GT
2GB 1066MHz DDR2 RAM
I feel like those setups were pretty comparable. A well-respected AMD dual-core vs. a well-respected Intel dual-core, motherboards of similar characteristics, identical RAM and video card. Quite simply, the Intel smoked the AMD. 3DMark06 gave them about equal performance, but the Intel rig absolutely destroyed the AMD rig when it came to gaming. Much smoother gameplay, less crashes, and overall better performance, even in regular OS use. For some reason, I just could not configure the AMD setup to work the way I wanted it to. It seemed to randomly freeze up when I could see no reason for it. It *may* have been a compatibility issue between the motherboard and the RAM, but the reviews that I'd read suggested that the Crucial Ballistix RAM I was using would work fine with the particular AMD mobo I chose. The only thing I've ever had to adjust in my Intel rig was the memory frequency, which I also had to do in the AMD rig, so that doesn't make any difference. Intel showed better, more consistent performance overall.
AMD is really struggling to keep up with Intel right now, especially with the disappointment that was their quad-core release. Granted, my experience may be an exception; I know a lot of people really support AMD, and if you've had a good experience with them, then that's good for you. But I'm just sharing what I saw from relatively similar setups.
Anyway, consider building your own, and consider looking at Intel.