I'd go with one of these for a prebuilt:
Add a 128MB 6600GT video card and a decent 19" LCD monitor (Samsung?). I'm not sure any of the prebuilt machines you get in the stores have power supplies that will react well to a 7800GT. Be prepared to swap in something decent like a Seasonic S12.
Athlon 64 3500+ or X2 3800+ dualcore
Pair of 512MB Crucial PC3200 DIMMs
7800GT video card
Probably a recent revision Antec case (make sure its PCIe capable)
ASUS nForce4 motherboard
NEC or Pioneer DVD burner
You get the idea. If you can squeeze the X2 CPU into your budget, get it. Dualcore rocks.
Ok, my system is about to die. Ive had troubles with my hard drive, cpu, gfx card, sound card, motherboard everything. Im doing everything i can each day to keep it running. So my sister is thinking about buying me a new one.
Now i have to pick which i want. She has 2 places i can get it from, frys or best buy, the reason for only 2 is since she has a card for each. So i have to go between the 2.
Now at best buy, the one im looking at is a Sony VAIO RB40 with 17" HS-Series Flat Panel LCD Display. Now my only problem with this one is the gfx card. heres the specs on the comp: