Custom Tab in the Inspector

Hey guys,

I'm digging on the subject for a while now but failed to produce and acceptable result.
The goal is simple :
http://blogs.unity3d.com/wp-content/uploads/2011/03/AddComponentButton1.png
*The button is not part of the AudioSource

It's pretty much creating a separate tab visible in the inspector of anything.

Cheers,
Jedy