I installed Windows 7 on my Boot Camp and installed Starcraft 2, after I click the icon of Starcraft2 it prompt out this error message:

"The videocard is not accessable because no display drivers are installed, another 3D application has exclusive access or the machine was locked. Please close any 3D applications or games and try starting Starcraft II again. If the problem persists, for more information consult our support website at http://starcraft2.com/support"

I'm using:
iMac 3.06GHz, Intel Core 2 Duo
4GB RAM
256 MB NVIDIA GeForce 9400

I think it suit enough to play Starcraft 2 unfortunately the above error message gave me some problem. I tried VMware fusion, Windows 7 play but the game is very slow because the graphics is shared within my iMac memory. Did anyone know how to solve this?

How to install bootcamp drivers on Windows 7?