Thanks Mnjul
It worked
What is the benefit of this by the way? I now have the Admin installation installing al the MP3! files in 'C:\Program Files\Messenger Plus! 3\' and the same programm files are now also in 'C:\Documents and Settings\Gast\Application Data\Messenger Plus! 3'. My HD is large enough, but it doesn't appear to be very efficient...
Also: Does this mean that when updating Plus! I have to update not only the Admin but also seperately the Guest account??