Anyone know how to fix lagginess?

[Mounce]

[UPDATE] - Seems the update I found in FAQS fixed 2 of my problems, so last is this.

Why is the game so laggy?! I can run games like Half-Life 2 max and I know this game runs great physics and calculations but so does Half-Life 2 but it seems to be laggy or choppy no matter what I do, it lags no matter what the settings are put to pretty much and to me the visuals arent that impressive so that it has to lag that badly. It's weird. It maybe runs below 25FPS

My computers specs are as follows incase this helps

Pentium 4 3.0GHz w/ Hyperthreading
1.5GB DDR RAM
ATI Radeon X1650 Pro

and Yes, right before I started to play the game just yesterday I had Updated my Graphics Drivers, so they are not outdated. I even reinstalled the game fully and it didn't help.