Try the Dell outlet. I bought my last 5 computers from them at incredibly low prices. The last one I got (about a month ago) would be right up your alley:

Core 2 Quad processor, Vista Premium 64 bit OS, 6 Gigs RAM, 750 Gig HD, Radeon HD 2600 XT video card (you can probably save a few bucks passing on the video card and picking one up from Newegg.com) for $600 shipped to my door.