This is very easy to do, if you are familiar with both a 3D application and DVD SP.
First you create the 3D scene with buttons in your 3D app and export it as a Quicktime movie.
You will probably want the button highlights to match the perspective of the buttons,right? In that case, still in the 3D app, create the highlights (with a black material), place a white background then turn off everything else (except highlights and white background). Set both the highlights and the background to ignore 3D illumination and use pure color instead. Export this as a PNG, TIFF, PICT, etc.
In DVD SP import the 3D movie and then assign the overlay map (the b&W image) for the highlights. I did this many, many times.
I know this post won't give you the step by step guide you would need, but at least you now know it's totally doable
Adolfo Rozenfeld
Buenos Aires - Argentina
www.adolforozenfeld.com