I've been through this in the last couple of weeks for an Ipaq, although I believe the principles are the same.

You can't map the keys in a visble way, you just have to remember the assignments in the earlier post. To program the rocker up key, assign actions to what ProntoEdit calls Volume +, for rocker down assign actions to Volume - etc etc.

I use left and far left for volume +/-, and right and far right for channel +/-

Have fun. Have you tried Tonto. Big improvement on Prontoedit!