I know how to set Super_L (WinKey) button to open the menu.
gconftool-2 --set /apps/metacity/global_keybindings/panel_main_menu --type string "Super_L"
Currently, in order to close that menu, I am having to mouse click outside the menu area. I need to use the Super_L as a toggle button. (pressing one time would open and pressing second time would close)
So what I need now is to be able to close it when pressing it second time.