Mention "stripping" and "wallpaper" in the same sentence and you're bound to hear groans. It's a messy, difficult job. However, there might be a way out. If your wallpaper is solidly adhered, you may be able to paint and plaster right over it. Your results will depend on how well you prepare the surface. Take the time to do it right, as the coatings of plaster and paint will make the wallpaper even more difficult to remove if you do the job improperly.
Press joint tape over the wallpaper seams. Seams allow moisture to seep in behind the wallpaper, weaken the paste and cause the wallpaper to loosen.
Load joint compound onto the trowel with the Spackle knife. Use the knife to scrape some compound off the trowel and smooth it over the joint tape, overlapping the edges of the tape. Scrape off the excess flush with the tape surface. Sand the edges after the compound dries completely, leaving as smooth and even a surface as possible.
Paint over the wallpaper with an oil-based primer to protect it from moisture in the plaster. Pour primer into the paint tray. Load the roller with paint. Roll it back and forth along the tray's ridges to remove excess paint. Use the paint roller for all except an inch or 2 around the perimeter of the walls. Use a brush for edges and corners. Allow the primer to dry thoroughly for the length of time the manufacturer recommends.
Apply the plaster according to the manufacturer's instructions. Load the plaster on the trowel with the Spackle knife. Use the knife to scrape some of the plaster from the trowel. Smooth the plaster on the walls. Allow it to dry thoroughly.
Paint the walls using a clean paint roller. Use the same technique used to apply the primer: roller for most of the wall surface and a brush for corners and trim. Allow the paint to dry.
Clean the paint rollers and brushes with paint thinner.
If the wallpaper bubbles after it's primed, cut out the bubbled part with a craft knife. Spackle the damaged area with joint compound. Sand and re-prime.
If the wallpaper is not firmly adhered to the wall, the weight of the plaster and paint could cause it to loosen and fall.