I've been running SC2 on Medium just because that's the "recommended for my computer" setting. I was wondering if I would be able to run it higher or not. I'm not too versed on computer hardware (or software, for that matter). So I'll do my best to describe my laptop.
Gateway FX P-7805u
IntelCore2Duo CPU P8400 @2.26GHz
4 GB RAM
Nividia GEFORCE 9800M GTS (1 GB)
286 GB HD (30.3 GB free)
Download Fraps and then change the settings in game. You're going to want atleast 30 FPS. You can also review some of the cinematics to see if it runs well there too. You can probably run the shaders on high, not sure if you can run everything else on high or not.
I doubt you could get Ultra going with decent framerates but High might be possible... The joy of PC gaming is you can set what you want. IMO try high and see how it runs. If it's not good, lower back to medium and set, let's say, Textures to High or Ultra which alone should make it look good. Maybe put some special effects up higher too, but leave shading and water at medium.