don't know..I have some Fujitsu Siemens's multimedia keyboard with about twenty extra buttons, and can use Gnome's prefences to assign commands to them except VolumeUp and VolumeDown buttons...I guess the others work. with those two, however, even though they're not assigned to anything (so they shouldn't do anything), I get an effect like I would press CTRL+ALT+F8; black screen, and get back to normal X server (F7) just by pressing CTRL+ALT+F7.
I'd too like to know what the heck is going on with these buttons...I guess something with the value they give when pressing, that seems to be the same as some key-combination..
not that I'd need these keys..but still