I just finished all the campaigns on my 15 i7 His-res MBP a few days ago, really good game and can't wait to see the following episodes.
I initially had lots of crashes during playing gameplay if I run everything at high settings using apple's boot camp nvidia drive under windows 7 ultimate. So I Googled and found newer nvidia drive may solve the crash issues, so I downloaded the newest 330M driver from nividia website (released in mid July) and installed the new driver, Starcraft II crashed much less now and the GPU temperature reduced from ~ 80 to 75 degrees. I also used GPU-Z to check the GPU statues during gaming, I think texture settings is the only thing that will affect the VRAM usage, the memory usage were ~320M and ~430M under medium and high quality at 1680*1050 respectively, consistent to their suggestions.
So if you want to use better texture probably you need the 512M VRAM in i7 MBP (I did not notice much difference between med and high texture settings although the VRAM usage changed dramatically). The 330M card seems to be fine running under all High settings after driver update. But due to the crashes I had before I normally run the game at high texture settings and everything else mid to make sure the card is safe. And due to reports that Starcraft II may damage your video card you'd better do so and put following line in your variables.txt file.
frameratecapglue=30
frameratecap=60