Fallout is one of my all time favorite games. It is a role playing/adventure game set in a post apocalyptic wasteland. You are a member of an underground vault that has survived a nuclear war, however due to mechanical failure your vault is about to run out of water. You are sent into the outside world to try and find the part needed to get water back to your vault. Needless to say things are not that simple, and you soon get embroiled in the affairs of the outside world.
One of the things that I appreciate about Fallout the most is the amount of freedom and gives you and how you solve the problems you encounter. You can play the game as a dumb muscle-bound fool, blowing up anything that comes in your way, or as an intelligence smooth talker (it is actually technically possible, though very hard, to complete this game without killing anyone).
Fallout runs well under Windows 98 in Virtual PC. It also runs well under Windows XP and Windows Vista when run directly, but I prefer to run it under Virtual PC as it only supports running at 640 by 480 resolution which looks kind of funky on my computer. By using Virtual PC I do not have to worry about this.