My approach to these sorts of scenarios:
Start with inexpensive but decent system, $354, http://www.ascendtech.us/customkititems.as...DTWINPHIIX37101
. System is purchased for MB, tower, Windows install. HD provided is a throw-in, PSU is going to be replaced by reliable PSU. Any RAM provided is a bonus, but RAM is not major consideration since 4GB of quality DDR2 can be had for about $50.
Determine what GPU gives you the best bang for the buck, buy as separate from Newegg, etc.
Obtain reliable PSU that fully supports your GPU.
That should get you there, with a backup PSU for emergencies.