Ok, well here's a simple checklist to go through (in order):
1. Re-install the game. If it works, great; if not, move on to step 2.
2. Make sure that you have downloaded and installed all of the Windows updates including the .NET frameworks (up to 1.1) from the Windows Update website.
3.Make sure you have the latest graphics drivers and control panel from ATI. You can get the latest ones for your card
here. (33Mb download). Requires that you have the downloads installed from step 2
4. Re-install the game again (making sure you restart the machine before AND after the installation).
5. If none of this works, then uninstall the game completely and defragment your hard disk and re-install one last time. If failure persists, return the game to where you got it.
This advice is very basic but it's the best starting point to finding a solution.
While I think of it, are you using any kind of Virus protection? I use Norton Antivirus and have no problems with any of my games but I know there are Antivirus packages out there which cause people nightmares.