Thanks for the very prompt answers chaps!

Copy the RTR Gold directory to a place somewhere else on your harddrive (after that make sure that it works).
Now you should have two working RTR Gold directorys.
Uninstall RTR from the original one. Now you should have a working RTW 1.2 directory (please check it) and a working RTR Gold.
I cant believe i didnt think of that!

Thanks a lot, my dad will be happy hes not losing his beloved Roman Empire

I'll give it a shot tommorow!