Upon upgrading to OS X 10.6.3, the P55 chipset was supported OutOfTheBox.
But there's a downside...
Apparently due to a Gigabyte BIOS bug, all SATA hard drives appear as External (Orange Icons).
While it's just a cosmetic issue, it affects the familiar feeling of the OS X desktop.
Several methods were developed to overcome this.
I'll briefly describe the options here, and present my own 'Vanilla' Solution.