I can help, i really enjoy blueprinting computers and would love to help, first do you want a monitor? A monitor could run half that budget or more $150-$1000. Do you want a new keyboard and mouse? They can cost $50-$200.

Here is the basic computer and then we can fill in the blanks:

CPU - really personal preference here either AMD or Intel. I prefer AMD for gaming due to the floating point decimal system AMD uses, which calculates into more math for reading graphics, but a powerful video card would do most all the calculations now days. $50-$500
MotherBoard - Id get an up to date board with SLi and room for expansion. $50-$200
VideoCard - you could get a cheap low budget 7300gt card for $75 or go higher for an 8800gt or 9800gt, $300-$700.
Power Supply - i would get an SLi ready PSU around 500w-700w, $50-$200
RAM - id reccomend 2GB minimum upto 4GB, $50-$200.
Hard Drive - you can get a 300GB for about $75-$100, or you could get smaller but more of them running in RAID, $50-$75 each.
DvD player/burner - you could get a burner/player for around $40-$60
Operating System - I run XP32sp2 and dont have any problems but you could run Vista32, up to you. $75-$150
Case - something cool that you would be proud of. $50-$100
I will blueprint you a decent build, to look over and have others make recommendations. I will post it shortly.