Did you update or register? because ur no supposed to do that
As I recall there should be an option to select the virtual disk once you hit the install extra languages.
I don't have Rosetta stone on me atm, so i don't know if I can be of any further help, but I when I did the install I just followed the instructions from that thread that I linked to and everything worked well.
Perhaps you should search/ask in that thread to see if you can solve your problem.