Question says all in itself. The walls are normal plaster, and there is horrid Wall paper attached to the outsides that was hidden under wooden panneling that we removed.
Score the wallpaper first, with a gadget available at the Wallpaper store. Then either use a steamer which you can rent, or use a bottle of liquid wallpaper stripper.
Using wallpaper stripper: Use a sponge or cloth to apply the stripper to the wallpaper and leave it on for the amount of time indicated on the bottle. Then use a wallpaper scraper to scrape it off. Use a wet towel to wipe off the remaining adhesive. This is the method I prefer but some prefer the steamer.
Using a steamer: Follow the directions that come with the steamer.