There aren't any yet, but I would compare the graphics to a game like Dawn of War II. Here are the specs for that game:
Minimum Requirements
* Windows XP SP2 or Windows Vista SP1
* P4 3.2 GHz (single core) or any Dual Core processor
* 1 GB RAM (XP), 1.5 GB RAM (Vista)
* A 128MB Video Card (Shader Model 3) - Nvidia GeForce 6600 GT / ATI X1600, or equivalent
* 5.5 GB of Hard Drive space
Recommended
* Windows XP SP2 or Windows Vista SP1
* AMD Athlon 64×2 4400+ or any Intel Core 2 Duo
* 2 GB RAM (XP and Vista)
* A 256MB Video Card (Shader Model 3) - Nvidia GeForce 7800 GT / ATI X1900, or equivalent
* 5.5 GB of Hard Drive space
I'm guessing here, but if you watch the videos for SC2 (
http://starcraft2.com/movies.xml) you can see the graphics are pretty impressive, even for an early build.