[CentOS] How do I create a new menu category in GNOME ?

Hi,

The title says it all. My GNOME desktop is in French, so here's what my 
standard Applications (same word in french) menu looks like :

Applications > Accessoires (Utilities)
              > Bureautique (Office)
              > Graphisme (Graphics)
              > Internet (Internet)
              > Son et vidéo (Sound and Video)

Now I'm currently installing a medical application (Medintux) which 
consists of several different "modules", e. g. programs where each one 
does one thing. There are something like ten different modules, and I'd 
like to create a new category in my main menu, so I have :

Applications > Medintux > User Management
                         > Diagnostics
                         > X-Rays
                         > Scanner management
                         > Prescriptions
                         > ...

Something like that.

I'm already familiar with creating *.desktop files and putting them in 
/usr/share/applications and running update-desktop-database. But I can't 
seem to be able to create a new category. I found some probably related 
files in /usr/share/desktop-directories and tried to edit my custom 
medintux.directory file, but to no avail.

Anyone here familiar with the innards of GNOME desktop menus?

Cheers,

Niki