The source of slowdown... after i tested my machine and reinstalled winxp a thousand of times, i realized that the best way to run the game is with the Nvidia drivers 52.xx (the ones before 53.03) and Directx 8.1 (the original that comes with XP). In the game, you must set the resolution the same as your desktop, and if you want the replays to be at normal speed, you have to set quality on LOW, wich means no shadows whatsoever,.. it looks a little bit strange at first, but you can get used to that easily.. anyway, if you like to play with shadows and all, put the detail on medium or high, and the game WONT slow down, but the replays will be useless (too slow!!!).
My equipment:
P4 2.0 Ghz
768 MB RAM
Sound blaster PCI 128
Nvidia Geforce 4 Ti 4600 64 MB
Directx 8.1 on WinXP
cheers.