michaelleung: I'd like to know as well, because I might be getting a MacBook soon and I also want to know if the new graphic cards are any good for gaming (GOG games, Orange Box, COD4, etc.)
If you're talking about the regular Macbook (not the Pro model w/ discrete graphics processor) then check out the following article:
http://optimitza.cat/news/2008/10/16/nvidia-geforce-9400m-benchmarks/ - it pretty much sums various reviews and benchmarks of GF 9400M that's built into the unibody MacBooks.
As for games available on GOG.com - there isn't a one answer as we have a pretty wide range of games with different system requirements and we do not support Macs unfortunately :(. From my own personal experience I can tell you that DOS-era games should work just fine via virtualization solution (I've tested few titles myself via Parallels app) while the newer games that use 3D acceleration will require dual-booting into XP / Vista (via BootCamp).
Banzaiaap: Hello all. I recently switched over to mac and I was wondering if and how I can run the games from Good Old Games on it. Is there going to be any support for it in the future?
Banzaiaap, currently we're focused on bringing more games to GOG.com catalogue and optimizing them for 100% compatibility with Windows. There's no official support for Mac OS, sorry :-(
PS: Don't get me wrong - lot's of people in our office are using macs (and gaming on macs!) and I'm pretty sure they'd love to play GOG games without using the 3rd party apps or dual-booting solution that was mentioned in the topic :). However, making these games work on OS X, as simple as it might sound, is not an easy task - both from software and licensing point - and it's definitely not a something you could expect anytime soon. Someday - maybe. Being a Mac user myself (and an optimist too :P) I keep the fingers crossed and wish for the best :)
