either put up new drywall over it, or paint over the existing wallpaper with an oil-based primer such as Kilz. DO NOT use a latex based primer. Once you've primed all of it, break out a sander and go over the rough spots. Then spackle the remaining blemishes and prime those again.
The bottom line is that you won't be able to scrape any of the wallpaper off of the drywall's paper layer. Let everything dry like I mentioned above, and then sand, spackle, sand, prime and repeat.