Actually my specs are:
Core2 Quad Q6600@3GHz
4Gb RAM
GeForce GTX 750Ti 2Gb
I believe they are more than enough. Btw I just play at 1680x1050 which is the maximum of my monitor (Samsung 226BW)
Usually those technical demos are just to show the best that the engine can do, so rarely you will see the same detail in real games.
When UrT HD is out, there should be more and cheaper hardware to run the game. Nothing to worry about.