I selected the Main Menu (editor) item from the Preferences group of the Main Menu itself.
This is the menueditor "alacarte"; he is only designed for editing Gnome-menu, not LXDE-menu.

Create a new entry in '/boot/grub/menu.lst' of your HD-installation and append at kernel-line "desktop=gnome".

Boot Gnome Desktop! Now all changes made with "alacarte" will be permanent in Gnome-menu (not in LXDE-Menu!).

Greetings Werner * http://www.wp-schulz.de/knoppix/summary.html
Own Rescue-CD with Knoppix (Knoppix V6.4.4 remaster)