I just tried the demo,I have to say a fun game.
After I load the map...for about 30 seconds it goes extremely choppy (around 2 fps) Then all of a sudden, picks up and I get 60. It's not a huge problem, just quite annoying and if I can get it fixed then that's awsome, if not then oh well.
My System Specs:
Pentium D 3.4 ghz
ATi Radeon X1950 pro
1.5 GB of RAM
I had the same problem. Downgrading my Catalyst drivers to 7.7 fixed the problem for me. Please be advised the demo officially requires Catalyst 7.9 or later to load but I managed to run it with the 7.7 without doing anything special. Also, since you have a X1950 (AGP I would wager) you should know that ATI recommends you stick with 7.7 in the release notes since there are (other) problems with that card with the latest 7.8 and 7.9 drivers.