Well you could do like I did and get a Dell computer. Check out
www.dell.com/outlet and choose one to your liking. Also, you can check around on the internet to get discount codes for refurbished desktops to make it even cheaper. I know what your thinking, "boo, a refurbished computer!" but hear me out. This is the second time I've went through dell outlet and was VERY pleased on both occasions. Dell's refurb computers are basically new computers and I highly recommend checking them out if you don't mind deleting extra crap off your HDD once you receive your computer (this time around, they had even less crap, very minimal to delete overal). I essentially wanted to just build my own computer and I do know how to (from swapping new hardware in and out of computers many times over the years) but I chose the dell route for a number of reasons.
This is what I was able to get and for how much. I got a Dell Inspiron 530, with a Intel Quad Core Q6600 processor, 3 gigs of RAM, 2 320 gig HDD's, 19 in one media card reader, 16x DVD/CD burner and Vista Home Premium. I chose this because it was a scratch and dent item (which drops the price even more) for $429. I was impatient and couldn't wait for a code, so with taxes and shipping it came to a total of $485. I then swapped out the power supply for a 500 watt PSU and added a 8800 GTS 320MB video card (PSU was $40 and video card I got at
www.fxvideocards.com for $87 shipped...it was a weekend special). I then bought a PCI slot cooler from newegg for $10 shipped bringing the grand total to $621. I'm happy with my purchase and that's pretty cheap for a decent gaming rig IMO, yes there's better graphics cards out now but for $87? :] I'm not complaining. The main reason I chose the Dell route was because if you were to build your computer for a reasonable, well very reasonable $600, near the same horsepower as mine...u would still then need to by a OS (Windows), so add on a extra $100-120. Plus you get a few other extras that I didn't mention buying from Dell including other software/keyboard/mouse/other shit etc.
The main thing you need to remember if you buy a Dell is, you can't overclock do to the motherboard and you won't be able to do SLI. I wasn't planning on doing either so Dell worked out good for me. I'll be honest, if your willing to spend more then I was, then building a custom computer is still your best bet. Me being extremely cheap and impatient, I'm happy with my computer decision/purchase. Oh, by the way, the "scratch and dent" that Dell marked for my computer is a joke. It has a "tiny" TINY little scratch on top of the case which easily knocked the price down a good $100 if not more. Heh, I got more scratches on the case opening it up installing the PSU/graphics card/slot cooler then that little thing :] Anyways, good luck with getting a new computer.