I expect Wolfenstein: Enemy Territory would be fine on a MacBook: other Quake 3 engine titles (universal binaries) perform VERY well on my X3100 MacBook Air. World of Padman for instance, looks superficially much more modern than W:ET, and runs well at high detail settings--except I choose 16-bit textures. (It makes little visible difference but runs much faster for some reason.)
I'd expect GMA950 could handle it too--maybe with different settings.
Now, if you're talking about the new Quake Wars: Enemy Territory, then no--its requirements are higher. That's a Doom 3 engine game, and although I can get those to run OK on my Air at LOW detail when not much action is happening (1v1 in Prey demo is OK--and doesn't look bad considering the low res I use), Quake Wars would not be happening.