How can I remove a dado strip of wallpaper without damaging the wall?
We used to carefully use water and it would come off pretty easily with some gentle scraping.  Just do not crazy soak the wall.  If you keep the wallpaper damp you should be able to carefully remove it with a scraper.  It should not hurt the drywall especially if there is paint on it.  Try this on a small area first.

Home Depot has a good description on other ways to do it.