Here's what I did, you might want to consider it also.
I bought a Compaq Presario PC, and as far as I've seen, no one can beat Compaq on prices. Interestingly enough when I tried to look up the prices of the components that came with the Compaq PC (on NewEgg), looking at the best deals available, they still somehow amounted to a little bit more than how much Compaq charged for their PC. So yes, amazing deal from Compaq! Dell doesn't use AMD so I don't even look at Dell at the moment. Here are the specs of what I got:
CPU: Athlon 64 3500+ (2.2Ghz)
RAM: 1 gig
HD: 200 gigs 7200 rpm SATA
Video Card: Really crappy integrated nvidia one (the only weak link).
PSU: Some 300 watt crap.
Came with Keyboard and Mouse.
This cost me about $550 total, shipping and all.
So now what I'm doing is upgrading the PSU to something like the Antec TP 430w and the video card to Geforce 7600GT. Both of these things together cost around $230 on newegg. Now I have a very good gaming machine and a great all around PC, all for a total of $780 or so.
Geforce 7600 GT is a good latest-gen midrange card, great bang for the buck, and the PSU I'm getting is enough to run it plus a little bit of overhead just in case. Unlikely that I'll ever upgrade this PC (except possibly ram to 2 gigs in a few months), as I will probably buy a new one in about a year and a half or so, for a similar price.
If you were to get a Geforce 7900GT or similar, you'd still be under $1000, and now u'd have a really kick-ass gaming machine. The 3500+ is basically the area right before the price becomes exponentially greater with only marginal performance increase. Considering the lifetime of this PC I didn't think dual-core was worthwhile just yet - but the next one will certainly be dual core, no question.
So basically I used a combination of purchasing a pre-built machine and manual upgrading after I got it to get a really good deal and a problem-free computer that works blazingly fast and does what I want it to do with no problems.
Just make sure to disable and uninstall all that useless software that is bundled with these PC's and runs on startup. I'm on a really limited budget, and I got the compaq PC right from a store (best buy), so no need to wait, except for the new PSU and GPU. I think I have a very good deal on my hands, and it's just one thing you may wanna consider doing as well. If anyone thinks that what I did wasn't a great idea though, let me know, since it's the first time I attempted something like this - so far though I've been impressed with the results and the cheapness of it all!
In fact, I wonder why more people don't do something similar? What is wrong, for example, with a computer from Dell or Compaq? If all the other parts are good/decent, and you can upgrade the terrible videocard they come with, why not? Similarly built computer from Alienware amounts to like 2x or 3x the price, and even more from Falcon Northwest, All American Computers, and others. So again, the absolutely unbelievable price you get from Compaq, combined with an additional videocard/PSU to replace the crappy ones it comes with, and it seems like u have a machine no worse than anyone who built theirs from scratch using equivalent components. Am I wrong?