Oohh, a problem I might recognize (surprising, being a bit of a

myself

). First of all, I've read that this sort of thing can happen with WineX, that apparently problems occur similar to those related to copy protection issues. Secondly, I know that sometimes when installing a game on Windows which is not from it's... eh... original media, the install will go just fine, but the CD will not be recognized as being in the drive.
So anyway, you might want to try a "No-CD fix." I know that there's a very large group of them
here, although that's a pretty annoying web site in my opinion (get ready to close a lot of pop-ups, lol). If the game you're talking about is "THIEF: THE DARK PROJECT v1.14" they have the no-cd thing for that
right here. Keep in mind i'm just getting started with WineX myself... i overwrote an exutable for a game I'm trying to get to run, Morrowind, with a no-cd "fix" from my other computer, and it seems to have gotten me a little further along, so I think that might work, but I still have yet to get it to run right
