NEOGAF may be loaded with console war in-fighting and Sony fanboys, but it's a really good source of news:
Unreal Tournament 3 Beta Demo Download Links:
Can my PC even run this? I guess I'll have to find out the hard way.
I saw these specs for one gamer who tried it and this is a picture of the graphics that he's getting:
Specs + UT3 == ....
And if you're one of the lucky ones with a super PC, you'll get graphics like this: