I noticed when I play, sometimes I get a really bad choppy frame rate, this seems to happen somewhat randomly, (as of right now I've noticed it the most in the Tora Bora level) and what little I've played the AW expansion seems to not suffer nearly as bad.
I did change the processor affinity settings, and this did stop the 'stutter' but everything seemed to move in a form slow motion. Which is to say that I and all of the other characters seem to move at about half speed. (Not for sure on before and after frame rates though, all I know is it's most certainly noticeable.)
As a second part to this question that is also related, I get SEVERE (as in not even playable) stutter when trying to connect to multiplayer games. I noticed that there was another chap who had a similar problem with same operating system (x64?). So I was wondering if anyone found a solution to that.
Below are my system specs, I know they aren't the greatest ever but I had my original retail (boxed) version of Postal 2 (original only no expansions) playing at really decent speeds and resolutions on an incredibly old P4, 128 MB GeForce FX, and 1 GB of RAM. So can someone help keep ME from going Postal? :)
System Specs:
2.8 GHz AMD X25400 Dual Core CPU
4 GB RAM
256 MB GeForce Card

Thanks Starkrun! That actually did the trick, once I installed that and changed the Affinity on my processor it actually ran better then it did on my old computer :) Sweet. But then I ran into a new problem. I'm going to start a separate question for this.