Karen, if you paint now, you will have a bigger problem down the road when you want to change the wall treatment again. It is better to fight through the problem now. Unless the paper that is on the walls is perfectly smooth and flat, any seams or joints will come through the paint. Have you tried a steamer?
Occasionally, people have put things like old worthless stock certificates on their walls using any old kind of glue. If this is the case, you might have to use a big, sharp chisel and try hard not to scratch the plaster since you will have to fill the scratches back up. If this is too much of a challenge, you might be better off putting up new, thin drywall. 3/8" thick and, I believe, 1/4" thick drywall is available in home centers.