I am trying to play the game but it seems to be kind of buggy. sometimes the game quits on me, other times I cant do certain things in the game like simply talk to people to get missions..after hitting the appropriate key?
maybe a driver problem. Try to update graphics and sound drivers.
If you have an add-in sound card, try to disable hardware sound processing (Vista nad Win7 doesn't allow sound cards to process by means of hardware)