Sancho, your plan is flawed. The GTX 670 can do about 200 kh/s, the 7990 can do over 1000 kh/s. So keep the GTX670 as your display driver and use the 7990 to mine. Of course, whether you can run AMD and Geforce on the same computer, which is probably what you're really asking, is harder to say.
Oh, I was definitely going to use the 7990 for mining as well as the display driver.
But yes, wondering if I can run them both on the same computer, thanks!
Running windows 7.