Ok then, let's try something else. Can you open up the Console application and then try re installing the SDK. Make sure the Console app is open and you can view it along side the installation wizard. The console app is a nice way to troubleshoot issues on the mac. More info about it here.
Let us know if you spot any logs related to AGS appear on the console.
1/13/13 10:50:37.213 AM Installer: CoreAnimation: warning, deleted thread with uncommitted CATransaction; set CA_DEBUG_TRANSACTIONS=1 in environment to log backtraces. 1/13/13 10:50:37.370 AM Installer: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.