I tried playing Fallout on my Mac a while back. I didn't have any issues with 256-color support, but it would crash after about a half hour of play, without fail. I tried uninstalling and reinstalling several times, but it always did the same thing. So I've never finished it. Still haven't tried playing Fallout 2.
But I'm ridiculously excited for New Vegas! I popped in Fallout 3 earlier today to test out my roommate's new projector and 7.1 surround system, and it was glorious.