GuiforDVDAuthor is a free authoring program that should be able to do this, though I'm not certain it can import vob files directly. You might have to run it through Vob2Mpg first, to get a single mpeg2 file from the dvd.

And there is always the free trial of DVDLab Pro. I know it can do this job, and the help file included with the program is excellent.

I also found a guide by blutach, showing how to use VobBlanker to add chapters if you want to look at that method: http://download.videohelp.com/jsoto/...ells/index.htm