AirPort 5.6 won't install under Mountain Lion, but it will run once it is.
Here are the basic steps to install version 5.6 under Mountain Lion using CharlesSoft's Pacifist:
- If you haven't already download the AirPort Utility disk image file directly from Apple Support Download
- Place the resultant AirPortUtility56.dmg file onto your Mac's Desktop.
- Run Pacifist.
- Click on the Open Package option. Find the disk image file that you just placed on your desktop, and then, click on Open.
- The utility is located as follows: Contents of AirPortUtility56.dmg > Contents of AirPortUtility56.pkg > Contents of AirPortUtility56Lion.pkg > Applications > Utilities > AirPort Utility 5.6.app
- Drag AirPort Utility 5.6.app to your Mac's /Applications/Utilities folder.
You can now run the AirPort Utility from the Utilities folder.