I installed the Gothic 3 and BF2142 demos on my C2D 2.33 GHz 15" MBP 256MB X1600.
BF2142 ran really smoothly actually.... in fact, it ran better than it does on my desktop PC (an AMD64 3400+ with a GeForce 6800GT AGP card). The only issue I noticed was some occasional audio popping, etc.
I ran it at a lower widescreen resolution (sorry, forget exactly what, but not native 1440x900) with high detail settings, and I was actually impressed that it looked pretty good, not blurry, etc.
Gothic 3 ran fairly well all things considering, but there was some slowdown, and also some audio popping, etc. I did run this at 1440x900. It's a little choppy in places, but I've noticed this same issue on my desktop, and heard that Gothic 3 seems to not exactly run well on just about anything, so I think it handled it pretty well all things being equal.