Call of Duty 2- MPB Core Duo

Hi everyone, I just received Call of Duty 2 for my MacBook Pro. After having my MBP for about six months now, I finally decided to check out how my lappy fares with some games on OSX and from what I had heard about the Mac version of CoD2, my MPB was very capable. So far I have been very impressed, it runs a little less fluid than the 360 version (but then again, that has a much better GPU and an extra processor-all of which have a higher clock speed).

My question is this: Is it normal to slow the game down a lot just to enable the high quality rendering mode? I can run everything on the highest settings except for the high quality rendering, and if I want to run that, I have to turn everything else on low just to get it to run at a semi-solid framerate. Is this just a limitation of my GPU/CPU or is it software/RAM based? Any help would be appreciated greatly.