umm quake 3 only allows mouse buttons 1,2,3 and 4. The only soloution i found around this, i dunno if its possible on the db, is to bind that button (mouse 5) to a letter or key on your keyboard in the db's drivers.

So for example have the db's mouse 5 the button you cant use etc bind to v

then i q3 simply make walk = v.

i dunno though if the db has the option in the drivers to bind any of it's buttons to other keys. i have a da you see.