if you don't mind adding some parts to it... I think currently the best deal around for a 'store bought' computer is waiting for the Dell 400SC small business server to come around on a good deal again... that server is exactly like a PC, has the same mobo as a Dell 8300 has an 8x AGP slot... and I think as of last week, deal might be dead now, but it will be coming around again... it was a Pent4 2.8Ghz, 800Mhz, 80GB 7200rpm, 128MB DDR400 for about $350, (onboard sound, onboard graphics). Find a copy of XP, because this has no operating system. IF you get 512MB DDR400 (2x 256 dual channel) for cheap say $70-80 and a video card, 9800, 9800pro, .... then you have a great system for WAY less then the $1000 the other makers would charge.
If you have questions, and is interested in this deal, check out fatwallet forums, search in the Deal Discussion section for "400SC" (aka use the search function)