Custom Dropdown in WordPress 3.x Menus

Hello i’m trying to get this kind of functionality on mouse over:
https://dl.dropbox.com/u/2582843/Screen%20shot%202011-07-17%20at%203.54.03%20PM.png

this is how the menus are organized in back end:
https://dl.dropbox.com/u/2582843/Screen%20shot%202011-07-17%20at%204.00.25%20PM.png

the one with the black font are children of Registration, and i would like to keep only the title. and the one with white are children of those black ones.

Does any of you know of a plugin that does anything like this, or where to start to get that kind of behavior ?
I looked to some custom walker_nav_menu but i’m not sure if that is the way to go.

Thanks in advance