I ran Unreal Tourney, and while it did not hang the OS, it ran like crap, I couldn't move and I could see the system mouse cursor in the game. Took forever to load and to exit as well... I think thats pushing Classic a bit far . (G4 450 128 ram)
The Quake 2 I was mentioned was the one designed for MacOS X. Though, it is interesting to see how well it classic games are handled, as this will certainly be a selling point for some home users. I'll create a new thread for the issue of classic games.