My best guess would be, that you would rip the first one into the default directory, then when that was done, move it to another directory. Then rip the other one into the now empty default directory. When it was done, put them together and burn. I believe the menus would be screwed up and it might not be playable in your home dvd player. This is just an opinion though. Maybe someone has a better idea? If not good luck, hope it works for you!