what you can do is just copy the two files out of the users/'username'/music/itunes folder, and paste them in your dummy account. Then change the permissions on your main accounts music folder to read only for everyone. That way when your dummy account's itunes will have the same playlists and songs. Then, if anyone messes with the playlists, just copy and paste the two orriginal files from your main account.
Make any sense, im really tired, so let me know if it made none...