OP seems to be confused.
When people say Mac's are better at doing graphics and stuff. They generally mean the software like Aperture / Photoshop / Quark etc..... is generally more geared towards mac's creative market.
Like Erich5h say's. That's not the same thing as 'game graphics'.
There are a number of reasons why mac's dont game.
1 - with only 4/5 % of desktop market
And then 'gaming' is an smaller niche of the mac market anway compared to pc.
2 - until the arrival of Intel they were based on completely different processing architecture
3 - direct X is a pc API, and since most games use direct X it makes porting a pain and expensive process, especially considering 1...
-----
If you wanted to do graphics 'work' welcome to mac
If you wanted to do graphics 'gaming' you should have bought a pc or at least an upgradeable mac so you can bung in a decent gpu and run windows.
------
next time remember - a bit of research before your purchase pay's dividends.