The only interface I know is the Asus XG station:http://www.asus.com/news_show.aspx?id=5369
It requires an expresscard slot, which no Mac is equipped with (Apple thought the artists wouldn't need one...now they can't even get photoshop CS4).
And, yes, your thoughts are true on C&C 3 - however, be careful on other games! Game boxes list desktop cards only!
A 9400M is NOT equivalent to a desktop 9400!
The "best graphics cards for the money" has a graphics card comparison table that lists what the 9400M is comparable to in the desktop world.