I had a similar problem with C2004 after upgrading my PC to an Athlon 3500 & Geforce 6600GT; what's your PC specs ? Is there anything in the readme under the dreaded "Known Issues" section ? Did you have the same problem with the C2005 demo ?
I didn't fancy the Xspeed (?) option to slow things down, but found that if you enable Vsync (right-click on the desktop, select Properties, then the Settings tab, then the Advanced button - should be in there somewhere, depending on your graphics card), then ensure you're running a sensible refresh rate e.g 75 or 85 Hz (same place, probably under the Monitor tab, or if you've got a Geforce card, there may be a seperate Refresh Rates option.), it did slow the game down somewhat.
Whilst it still sped up a bit in places, it was a little more playable.
Hope this helps !