When you were installing you had the option under drivers to use the nVidia EFI driver. You should have selected that.

You can still install that driver. Insert the install disc and boot from it. Go through the install process. But this time under the customize DESELECT everything, except the nVidia EFI driver. Run the install process, reboot when completed, and presto! Your video drivers should be working. You'll want to download something called "OSX86 Tools" and enable the Quartz system. This will improve your graphics experience.