It's difficult to tell exactly, but you have to remember that DVD SP supports the feature set of Photoshop 5. Any elements that make use of later features (layer effects or styles, vector shapes, etc) will render wrongly. If you're using that kind of features, you will have to force PS to rasterize them (one way of doing this is merging that layer with an empty one).
Also, DVD SP apparently handles PSD layers by their index/stacking number, not their names. So , when you modify a PSD file that's already in use in DVD SP, you have to be careful not to insert new layers in the middle of the stack, but rather on top.
Hope this helps.
Adolfo Rozenfeld
Buenos Aires - Argentina
www.adolforozenfeld.com