DarkBlizz

It's not the processor , it's low memory problem , how much memory u have ?

I had 2 GB last month , SC2 lagged and like it had stops for 5 seconds at times , now i upgraded with another dominators , and have 4 GB , have win x64 and I disabled page file ,  SC2 loads fast , no lag at all nor temporary freezes.

I have quite high end PC , quad q9300  , gigabyte ga-p35-ds4 , enermax 620W liberty dxx , WD 500GB ,  HD 4870
And I had similar problems for 1 and a half years because i had only 2 GB ram.

Anyways , it's not your processor. And it's not SC2 compatability , it's a beta , but anyways , what a lot of people mistake , SC2 is a big game , it's just so hungry but you can still make good fps. 

Lowering the graphics won't help much , since your GPU is good enough , has enough video ram , but it's the virtual memory that's making this pain in the ass, HDD is too slow obviously.

EDIT: Oh you have 4 GB
 
  What operating system u have ?

Then just disable page file , win7=
- Right click on my computer and select properties , or go to control panel and click system
- click advanced system settings in top left side of the window , last button.
-select advanced tab in the new window if it's not already selected
-click setting in performance
-select advanced tab in new window
-click "change" button below in "virtual memory"
-select a drive in new window , then click the "no paging file" radio button , then click "Set"
-do  that for all drives , no paging file , 0
-apply ok , restart pc.
-no more freezes, and the overall PC boost will be huge.

in xp u have the same process but u skip second step.

If you did it correctly you will notice the change immediately after restart.

It still does have bugs , starting positions, are screwed up,  to get the same team in on to same side u must use computer 2 and 3 , and computer 4 as your ally or else it won't work , and then don't use startpoints , the team have some sort of start position override or what.

btw i have win7 x64