Ho !
I've got exactly the same problem:

I have a microsoft natural multimedia keyboard, (this thing) and I used a lot the special keys for sound and volume.

Unfortunately it doesn't work with litestep: I see the volume bar popping on the screen or the color changing telling it's muted, but no changes.

I use the last drivers intellipoint from Microsoft (if i remove it, it doesn't work even with windows shell), and i've tested another keyboard (an old natural keyboard with also the mute button) = same thing.

Any idea to solve this?
Are microsoft dumb enough to link the drivers of their keyboard to their own shell?

Well, there is an answer there: http://www.litestep.net/index.php?section=4&action=view&catId=3&id=4954&hl=

but i don't understand how to find the vkcode of all keys...