Our colleagues over at pcgameshardware.de have managed to do some benchmarking on Bioware's upcoming PC version of Mass Effect. Pcgameshardware.de benched this game on various CPUs and a lot of graphics cards from both green and red camp.
Bioware's Mass Effect uses Epic's modified engine which keeps the requirements at a moderate level, so basically if your system managed to cope with Unreal Tournament 3, you are all set to play Mass Effect too.
According to their testing, a dual-core processor is recommended, whereas quad-cores aren't providing any noticeable benefits. As for the graphics cards, Nvidia's 8800GT will be enough for 1,280x1,024 as long as you don't get cocky with anisotropic filtering.
The PC version of Mass Effect is scheduled to be released on May 28th for North America and June 6th for Europe. You can check out some screenshots and the benchmark results here.