Is it possible to run 32-bit only screen savers in Mountain Lion?
Just opening /System/Library/Frameworks/ScreenSaver.framework/Versions/A/Resources/ScreenSaverEngine.app in 32-bit mode doesn't run 32-bit only screen savers.
I don't think you can do this. I believe that Mountain Lion is 64-bit only, since my old Mac Pro, which is technically 64-bit capable, but won't run Mountain Lion. Lion could be booted into 32-bit mode, but I don't think Mountain Lion can.