i just downloaded arcanum demo to see if it works fine, and it didnt.. i had the same problem, than i opened it (the demo) with safe mod and it worked fine..
but still, i wont play the demo i just tried to search on google "arcanum safe mod download" and came to this link: Dimensions of Arcanum - General Game FAQ
than i saw on the "HELP INSTALLING THE GAME" this "arcanum.exe -no3d" thing,i did it and it just works fine now..