Special key mappings... is this possible

I want to remap the actions of my number pad keys when numlock is turned off (I'm on windows vista). I found a program called sharp keys, but according to it I'm pressing the same key regardless of the numlock status.

So I'm guessing I need to find something that modifies the action at a higher level than sharp keys. I'm not sure where to start to find something like that. This seems to not be a very common thing people want to do, so google has nothing on it.

Does anyone know of registry values or something I should edit? or prefereblly a program to edit whatever for me?