ACtually, you can increase vram on a mac via terminal. I used these codes to do mine and now i can play COD4 on my mac without any lag or it quitting on me. Type these codes into terminal. It might ask for your password though:
$cd /usr/lib
$sudo cp libcrypto.0.9.dylib libcrypto.0.9.dylib.old
$sudo cp libssl.0.9.dylib libssl.0.9.dylib.old
$sudo ln -sf libcrypto.0.9.7.dylib libcrypto.0.9.dylib
$sudo ln -sf libssl.0.9.7.dylib libssl.0.9.dylib
Dont copy the dollar signs, they just mean you have to press enter and its a new line there. after your done, reboot your computer and voila! ur done!
Do this at your own risk, if you mess up, your computer is pretty much screwed. These codes take away the barrier that allocates only 64
mb of vram for the mac and increases it to some amount. i forgot. so try it ppl and tell me how it goes!
Good luck!