how to map apple key to ALT with xmodmap

[Pander]

Hi all,

I have this in my xmodmap file:
!! map both [APPLE] keys to [left ALT]
!TODO does not work
keycode 115 = Alt_L

but it doesn't work and my left had is getting tired of ALT-TAB without 
the help of my right hand.

Does anybody know how to fix this (I use Gnome bby the way).

Thanks,

Pander