According to Midway, the actual official system requirements are a lot more lightweight than you'd expect. As far as RAM, CPU and GPU go, even run of the mill hardware meets the minimum requirements of 512MB, 2GHz and a GeForce 6200 / Radeon 9600.
Even their “Recommended” requirements aren't far out there, with Midway suggesting a 2.4GHz CPU and a gig of RAM. The GPU gets a considerable boost in that context, with them suggesting a 7800 GTX or x1300 card or better. However, even those specs were common in hardware over a year ago. This bodes well for the game itself, as well as other games based on the UE3 engine. At the very least, it looks like many Unreal fans will not have to upgrade just to play UT3.