How about this setup.....
Pentium 4 2.4 ghz w/HT S478
Some cheap mobo
512mb PC-3200 Mushkin
40 or 80gb HD. IDE 7200RPM
and a case that is simple, no windows or lights.
Oh and a Radeon 9200
That setup should be really really cheap. Now you can take $100-200 for yourself for just building the damn thing.