This guide uses the GOG version of the game however the Steam version is probably fine too. if that doesn't work then a fresh windows install may solve your problems and trust me, I literally did this to get this game to run properly once. I recommend that if you begin to run out of patience (for me that was after 10 minutes) then try a clean reinstall of the game. Sometimes installation goes perfectly and the game runs fine, however other times the game just won't work properly and you will end up spending days trying to troubleshoot a game that crashes or spits out error messages.
No matter which version you have you can always gain access to the GOG copy of the game by following these steps. Firstly there are three different versions of the game one bought through GOG, the other bought through Steam and a final version sold as a retail copy. Ok this seems like a straightforward process, however it can prove to be anything but easy.