One thing with System Shock 2 (Thief and Thief 2 have the same 'bug') which might have been mentioned already in the thread - it crashes with Hyper Threading (maybe with dual-core too). Turn HT off in your bios. Or alt-tab out when you get to the main menu, press ctrl-alt-del, find Shock2.exe in the list of running processes, right click on it, click 'set affinity' and disable the 2nd CPU for that exe. Then it will run without crashing but you need to do that every time.
Still my favourite game of all time SS2, followed closely by Thief and Thief 2. Can't wait for the spiritual successor Bioshock from Irrational (who co-created SS2 with LG). The RPG elements made SS2 so much more interesting than if it had been just a shooter. Very scary, great story, perfect gameplay (non linear too), great villain, endlessly fascinating and can be played in many different ways. Best interface I've seen in a game too. Brilliant sound (also excellent voice acting), excellent graphics for it's time.
Also after the official patch it has co-op multiplayer, which is just awesome fun. Best co-op game ever by miles. I've finished the game with my brother on co-op (on hard), and as all three characters on single player (again on hard). Don't play on medium btw.
If only every game was this good.