To the OP:
Yes, I think a new 13" MBP w/ 320M will run SC2 at low to medium-ish settings comfortably. When the graphics are low, the game really knows how to chop itself down. Blizzard has always been good at incorporating lower end computers with lower graphics possibilities.
I'd just like to contribute my experiences with SC2.
I'm running it on
17" MBP
2.8 GHz
9600M GT
4 GB
On Windows 7 Professional 64-bit (32 GB partition)
At 1920x1200x32 with all graphics options set to the highest possibility except shaders, lighting, and shadows (those three being set to "low"), I get extremely smooth game play without a single drop in frames.
Once I turn on any of those three, the game will be choppy albeit playable. The higher you go, it'll eventually become not playable.
Kind of off topic, but does anyone know how the 9600M GT would compare to the new 330M in performance? I'd imagine the change would be pretty small, but anyone fill me in?
Thanks