
I suggest you remove everything you installed and redo the whole installation according to the mac installation tutorial video here:
http://www.refractivesoftware.com/demotutorial_mac.html
That's a demo of an installation on a brand new Snow Leopard machine.
Since you have 2 different cards SLI won't work, so it should be disabled by default.
If you do find any SLI related controls, turn them all off. (However i haven't found any SLI controls on mac myself, i'd be interested in knowing where they are or a screenshot of them

And, before you begin testing, use a simple scene out of our testsuite, like the chessscene.
Yours,
Radiance