Skinnable GUI.. suggestions?

I'm working on an application with a semi-skinnable gui. QT4 has helped greatly (alpha blending, etc, etc).

I'm looking at how to animate certain elements of the application. For example, I'm using a widget stack to divide functionality into seperate sections. To go from section to section.. I would like to have one section slide off, and another slide on. Kind of like how the Tivo or XBox360 interface works. Unfortunatly, moving a widget with a transparent background is slow, and is very choppy (background jumps around).

Anybody have any suggestions?

-Chris