Well, it will play on GeForce 6 and 7 hardware, but only if you consider playing it being 1024x768 or lower, combination of low/medium settings, no HDR, and no soft shadows. Textures will definately have to be set to low on GeForce 6 hardware because get this, they are rendered at a resolution of 2048x2048! Compare that to the 256x256 textures provided by Doom 3.
Plus, UT2007 is going to be marketted primarily for the Xbox360. It will be a reward to be able to play it on the PC.