According to the audio interview that Mark Rein did, the Unreal Engine 3.0 tech demo was on an AMD 64 FX-53 or 55 and a pair of prototype SLI 512MB 6800 Ultra.
The demo was run in 1280 x 1024 and got just over 30 frames per second.
Now, obviously, that doesn't tell you much about actual gameplay or any optimizations that they may implement in the mean time. But it does let you know that you're going to be able to push your brand new top of the line PC to the limit with this game.
I trust that reasonably lowered details and resolutions will be able to be run on mere mortal PCs.