Right now as far as I know, there is no included code in the aquarium yet to handle logo's. People are just hacking things to get them to work.
The only way currently you can get something displayed is to get the latest version, install your logo, delete the one Jim has there, and then rename yours to exactly what Jim's was. You can't change between multiple personal logo's yet, because the only one that can display so far is using the name of Jim's until code is programmed to allow more than one.
You can change between the MA3 logo, and your "one" personal logo by hitting the "L" key, which works fine for me.
It works for you but does not work for me. Apparently there is something wrong with the code or I am missing something obvious. Are you running XP or Vista? Do you have your personal logo in the windows directory?