Painting - painting on plastic

I want to paint a room that is currently wallpapered. When I strip off the wall paper the wall underneath it will be rough. Is there a product that I can apply over it before I paint that will smooth it out or do I have to sand it down. If possible I'd like to avoid the latter.

Does anyone know of a paint or primer product that allows "slick" plastic to be painted?

If so, do you need to sand the plastic first and after paint is applied, what do you recommend to seal it?

Thanks

ecoplnd, When you remove this paper, is it leaving the backing on the wall, most of the time to remove this backing just take a sponge and water and wet the wall, let it sit for about 5 minutes and try to peel it off. Try this and post back with the results.

prkrafft, There are types of plastic out there that will not hold paint for a duration, especially if the plastic is plyable or soft, the best thing I coulod recomend is going to http://www.zinsser.com and checking out some of there products.

http://www.geocities.com/heychipster/painter.jpg