As a follow-up to my original post, it turned out the problem I was experiencing was down to my anti-virus having a problem with one files being downloaded and quarantining it, which would cause the download to fail at the end. To get the game installed I had to switch off my antivirus, completely remove the failed download from the queue in Galaxy, delete the files that had been downloaded from the Galaxy temp folder, and restart my computer
On an unrelated note, once I got the game installed and tried to run it, I bizarrely had a message pop up asking me to insert disk 2 of the game. Rolling back to 1.1 sorted this issue.
While I also got the game working I had to launch the 'Set up' launcher and switch 3D acceleration off. May have also been due to anti-virus but it happened even when I completely uninstalled all anti-virus so I think from reading your post I may have not deleted the old installation before attempting to run the game.