What Joe said; If pressing menu doesn't work, chapter skip, nothing there, fast forward.
There are certain DVD players that will skip through this mess pretty much no matter what. I've seen DVD players advertised in that they make it so you can skip through "unskippable" preview stuff.
Never encountered previews I've been forced to watch. When previews appear, and pressing menu does nothing, I skip through them of fast forward.
If I know ahead of time a disc has some unskippable advertisement, I load the dvd, get something to drink, etc. By the time I'm back the DVD is at the menu.