As far as my knowledge goes, Win 8 has a different primal structure compared to Win 7, that's why the first version of Win 8 was unable to run most if not all games that weren't specifically programmed to be run on it, and in general, a lot of programs didn't ran on it because of the same problem, they weren't compiled to run on it. To make matters worst, it didn't have a good compatibility mode (if it had any at the moment I got it, I didn't even bothered to "play" with it) so I "downgraded" to Win 7, which took me a whole day, because Windows folks a pretty smart and made their own O.S. incompatible between them (unless you were using a Virtual Machine to run one on the other).
The game is old, if I don't remember wrong, it was first printed on 2003, and reprinted on 2005, either case, the game is old and if you made it run on Win 8.X it's something. To be sure about why it is running slow open it and look how much RAM it's consuming, if the amount goes over 100 Mb, then the game is consuming a lot of resources just to run, if it's not that, then I'm at a loss on what could be causing it to run slow.
Anyway, tell me how it goes, I'll search for a solution in the meantime, though I don't promise anything this time, Win 8 is a really bothersome O.S. to deal with :).