The glow effect is actually already there, just hiding behind the buttons. What you nedd to do is replace the taskbar button image with semi transparent buttons so that the glow shows through.
You'll also need to skin the section Mouseover Mask. This controls the shape of the glow effect (the color of the glow is defined by the app that is open at the time and cannot be changed)
The mask should be the same size and shape of the taskbar buttons and have the same amount of states. In essence, make a copy of the buttons and fill it with solid black.
