Georgian was made part of Unicode over 10 years ago. Though OS X has never included fonts or keyboards for this script, some have been available via downloading from the internet to enable a basic level of support. Thanks to Reno Siradze there is now a much more advanced and refined set of tools for Georgian, which you can get here:
Georgian Language Kit 1.0
For more good Georgian fonts, try BPG-InfoTech
Note that it is customary in Georgian headings, ads, captions, and titles to use a special capitalized version of the normal unicameral alphabet (called the Didi style of Mkhedruli or the Mtavruli style of Mkhedruli). Inputting this style requires switching to a special font, although some fonts like those from BPG put this type style in the 10A0 range in place of what is supposed to be there.
Note Added Later: OS X 10.5 Leopard does include one font with Georgian, namely Arial Unicode.