HA! Fixed it!
I started the program with admin rights and under windows 7 compatibility and waited until it asked for the language to use. Using process viewer I could see that the process was called Engine.exe
I then changed to the administrator account (the search didn't find anything as my non-privledged account) and ran a search across my box for engine.exe - found in application_data under a folder called SETUP_40459. Copied that folder somewhere else then logged back in to my standard account. Finished the unworking installer. Changed into my copied directory, changed compatibility settings on Engine.exe - run Engine.exe and it installs like a charm.
What an annoying workaround to get the thing to install!!!