Before I upgraded to Mountain Lion and bought PSE 11, I checked to make sure they were compatible. Sure enough, on the Photoshop package it says it runs on" Mac OS v. 10.6 through v. 10.8". At the beginning of my "installation" I got a message saying I couldn't use the PSE 11 Install application "because Power PC applications are no longer supported." When I researched this problem online I found that all the geeks know that you can't install PSE 11 on a Mac running Mountain Lion because Mac no longer has Rosetta, a dynamic binary translator for Mac OSX that allowed Power PC applications to run.
Since Rosetta hasn't been on new Macs since Snow Leopard (2008), wouldn't you think Adobe would invent an Install.app that wasn't Power PC? Or do they hate Apple? (I've heard they do.)