You can get COD2 for Mac via Amazon direct download for $14.98. After seeing that it was in the Mac App Store it caught my attention, but I would never pay the hefty price tag Apple sticks on all of the better/more fun games.
I'm playing it right now at 720p and everything is flawless, except occasionally if the battles get intense with lots of people firing there is a minor lag, but nothing fatal. I mean, what do you expect from a UB game?
I could probably run it at 1080p, but haven't gotten around to changing the display setting. Will try it now and play a level and then report back. Surely it'll be a breeze for my 2010 mini, given that the game is so old, and I have an SSD and 8GB RAM.
EDIT 1: I should mention that I am playing the game while running the latest version of OS X Lion. It hasn't given me any issues whatsoever, so I conclude that Amazon's download is Lion-friendly. While on topic about Lion-friendly, I have read that Call of Duty and Call of Duty United Defense are not compatible with Lion. I was going to get those games as well last night but read that they were incompatible.