I'm not sure if it's just that the DVD Player version that comes default with Snow Leopard 10.6 is a newer version than the one in Leopard 10.5 but the good news is that it's less finicky than before.
Before I'd have to edit the DVDplayback file to use it to play DVD's. Also it won't start without plugging the external DVD drive itself into one of the USB's.
But now, in Snow Leopard, that trouble is now a thing of the (Leopard) past. DVDPlayer loads without any complaints at all; even without an external DVD drive plugged in.