ljyoun: Do you have to have mac 10.7 to play this? Why can't you play on 10.6? Also, why are intel integrated cards not supported?
For OS X, the officially stated Mac system requirements come from the Mac configurations they have in their QA labs. In other words, they've tested and verified that the game will work only on the configurations they have listed.
That's not to say that they won't work on other Macs though. System Shock 2 (which works excellently on lower-end Macs with GMA 950 graphics) is my favorite example of this.
Seeing as how (a) GOG simply uses Wineskin wrappers for their WINE-based ports, and WINE does work on 10.6, and (b) other games I've tested and played which use the Quake 2 engine from GOG (Daikatana, Kingpin: Life of Crime) work very well on Macs with the GMA 950, I'd wager that SiN Gold would work well on your Mac. Posting your actual system specs would be helpful though.
NB: I'm playing this on a 2010 11.6" MacBook Air with a 1.4 Ghz Core 2 Duo, and the game runs just fine. If it'll run on this Mac, it'll run on yours.