According to the Wikipedia page on id Tech 4, it needs a card of the GeForce 3/Radeon 8500 generation with a minimum of 64MB, and the recommended card is more like a 128MB Radeon 9700. Sounds like CPU horsepower is a lot less significant than I remember hearing at the time of release, but the alleged requirement is a 1.5GHz CPU (x86,) so there's your basis for comparison.
I remember my 3.4 GHz lappie with 128 MB go5700 ran it pretty choppy so probably the minimum cards mentioned don't do it too well.
