Is there a way to install Xcode 4.2 on OS X 10.8?
I need to compile some Firemonkey projects on my MBP (latest without retina) and I have OS X 10.8 installed and through normal means it's not possible to install Xcode 4.2.
No, you can't run Xcode 4.2 on OS X 10.8 (Mountain Lion).
Xcode 4.2 is available as a download from the developer site at Apple:
but it needs Lion.
If you need Xcode 4.2 you will need to install Lion, preferably on an external harddrive to avoid overwriting your current Mountain Lion installation.
There's answer on Apple discussions groups to install Mac OS X Lion into virtual machine to use previous FM-ios.
PS: You're allowed to install Mac OS X in virtual machine on Apple hardware which meets requirements.