This is one of a number of pages about installing Kubuntu Linux on a Sony TX1XP laptop. To see the other pages go here
The info on this page is all via Alexander Stefanescu. Thanks! Note he's using 6.06 Dapper Drake and Ubuntu (rather than Kubuntu) fwiw.
I figured out that in ubuntu's standard configuration Fn-F2 is mute, Fn-F3 is Volume down and Fn-F4 is Volume up. This is indeed handy, since the volume buttons on the side of the machine don't work (they give the same keycode as the "AV-Mode" Button)
Fn-F5 and Fn-F6 work as expected to dim the screen, Fn-F12 works as expected to activate suspend-to-disk.
I could find no other interesting Fn-combos.