AIR install problem with MAC PowerPC / Leopard
Windows 2000 and Mac PowerPC are not supported with AIR 2. Users can install and run AIR 1.5 applications, but will not be able to install or update to AIR 2.
Source – http://www.adobe.com/products/air/systemreqs/
The below are the links to be used for MAC – AIR 1.5 installer