This has been an issue for me with an older XP laptop running earlier betas, and now my new Vista desktop running the latest beta. If you go back to the main menu from within the game, it will let you start a new game or load a save, but will nearly always crash on the first turn. Loading a save of the current game from within the game works a little better, but things still happen (e.g. placing a spy crashes the game, all ships give you the 'lost in space' message when you try to move them, etc.). If I'm not pleased with the direction a game is taking, I have to quit the application, and come back in. Vista, or perhaps the latest beta, sometimes gets cranky and crashes the game if you repeatedly ctrl-N.