Don't know if this was the cause of your problem or not but....
Hitman 2: Silent Assassin does NOT like it if you switch to another program while it is open (using alt/tab). If you do this, 99% of the time you will experience double speed or an outright crash. Switching from game mode to another program while playing or paused will cause problems in most games.
In Hitman 2, this problem is also noted in conjunction with some of the cheats...but as previously noted, all you need to do is close the game and restart it.