If the wallpaper is peeling at all, don't do it! I really don't like the idea of doing it even if it is in good shape. However, if you are set on painting it, use a high quality primer with a leveling agent in it to smooth out any visual seems from the wall paper.
Richard, here is your answer:
My advice about painting over wallpaper is simply not to do it. Remove the wallpaper instead. No matter how tight the paper is to the wall, it still usually looks like painted wallpaper. Many times the seams between the sheets of paper stand right out, even when still glued down well.
Well you can paint over wallpaper. But the paint usually acts as a remover. I like to texture first then paint. Either a knock down, skimcoat, or eggshell. Then you don't see the lines. If you don't want to texture then prime first......
If you want even more people to tell you not to paint over wallpaper, search for paint over wallpaper in the "search posts" box at the top of the page. There have been a few posts about this, with a long string of opinions on a couple of them.
tried this years ago and I ended up stripping the original paper...double the work....the new paint caused the paper to bubble and come loose at the seams
Richard, I have painted it many times. As mentioned, the stipulation is that it is tight with almost zero bubbling or edge peeling. Shave any curling edges off, including running a razor blade flat along all seams. Then prime with oil primer and skim the seams smooth with compound if you are capable, if not use the high solids primer or texture paint or both.
I would also not recommend painting over wallpaper. It might look fine the first day but then may develop bubbles or the weight of the paint pull the paper from the wall. If you need help in removing wallpaper, here is a step-by-step guide I wrote that can help http://oconnorspainting.wordpress.com/2010/07/28/how-to%E2%80%A6wallpaper/