Leroux: Yes, I've used the 64-bit custom installer - without it I wouldn't have been able to even install the game. IIRC, I didn't download anything else though. The issue I'm having with the game is that it's slow, lagging badly and doesn't play smoothly. Which Ultimate Pack are you referring to? I couldn't find it among the downloads.
Ah, for some reason it's not there after all - apparently it's a TPB link. Nonetheless, it's pretty much the only viable way to get it working on modern OSs. I could have sworn I'd downloaded it from the Claw Recluse.
As far as lagginess is concerned, have you tried one of the alternative DirectDraw DLLs like ddhack or cnc-ddraw? Chances are you get some kind of error message, but it's always worth a try.