Here is one place to do some research

http://www.tomshardware.com/reviews/gaming-graphics,1786.html

GTX 280                                       - $375 after rebate.
Dual core E8600 or Quad Q9550 CPU (coin toss) - $270-$320
2x1GB DDR2-1066                               - $ 33
Motherboard LGA775 P45 DDR2                   - $120-$160

Power supply - 13.9A CPU (50% overclock assumed)
plus 15.9A video card (overclock version)
plus 3A single HDD,ODD, and fans
PC Power & Cooling S61EPS 610W (12V @ 49A) $80 after rebate

http://www.pcpower.com/downloads/s610_harness_3825.JPG

For a CPU cooler, you can use the retail Intel cooler to start,
or this one is a "blow downwards" style cooler, which might
keep any adjacent chipset heatsinks cooler. I like coolers
that bolt on, because you can adjust the screws for just
enough tension to hold it in place, without bending the
motherboard.

http://www.newegg.com/Product/Product.aspx?Item=N82E16835103046

All components selected assuming a single card graphics solution
(no SLI or Crossfire). The power supply is picked just to
run the one card, and has just enough connectors to do that.
The next model up (750W) has more connectors and isn't much more
expensive, after rebate.

You'll have to read some gaming type reviews, to decide
whether an overclocked dual core or quad core is the
right answer for a CPU. It might depend on the game,
as to whether the game makes good use of the CPU selected
or not.

The above also assumes you are running a 32 bit OS,
and the video card uses 1GB address space, plus the
2GB memory, uses 3GB of 4GB address space. My hope is
the 2x1GB memory configuration, is more agreeable to the
chipset.

For the motherboard, there are too many to review.
I was thinking about something P45 based, as cheap
and allowing some overclock.

Total around ~$1000 (or less, depending on taste). Assumes
you keep the old computer case, hard drive, optical drive,
keyboard, mouse, copy of WinXP etc. Otherwise, they're going
to chew into your CPU budget, and mean more overclocking,
plus an even cheaper motherboard. A G31 based motherboard
starts at $50 for example.

   Paul

Pricewatch.com