USE AT YOUR OWN RISK!

open regedit
1) go to HKEY_LOCAL_MACHINE\SOFTWARE
2) create a key ATK0100
3) go into that and add two string values:
EMAIL_KEY
INTERNET_KEY

and as the data add the program that you want to run.

WARNING: If the program you enter doesn't exist, the application will hang and you will have to go to the task manager and terminate it yourself, and restart it.

If you want to revert the keys to their normal use (the default mail and internet program) just remove or rename those registry values.

I will be trying to edit the Hcontrol application to make the side keys work with winamp too.