Depends whether you are building it, getting it off a custom site, or getting a Dell XPS. But if you were to build it yourself, you would be looking at an AMD Athlon X2 4600ish, 2GB RAM, SLI 7900GTs, something like that. If I had the time I would build one for you, but I don't right now.
I have no idea what the Conroe prices are, but you might want to wait for them to come out, or at least for the AMD price drop.