Windows 7: Change Caps Lock key to a very new key unused from everywhere

Hello !

I'm playing a lot and when using mumble, I use a "Push to talk" function.
The problem is that I need a key which interacts with nothing else, as I also talk when on IRC, on browsing the net.

Does anyone know how to create another key (brand new, without any use) so I can use it on Mumble as Push-to-Talk key ?

Thanks in advance for help

I would suggest using the Scroll Lock key. This post suggests a small utility to help do this: Map Any Key to Any Key on Windows 7 / XP / Vista - How-To Geek