Bump. I need info on this as well..except that I will strip wall paper first. Not a good idea to texture over Wall paper I have been told by the pros.
mrao77

It's true it's best to remove the wallpaper, but if you have 2-3 coats of paint on top of it already and you don't have any seams popping or corners coming up, then I would say it is stuck. Generally, you will want to prime with Gardz first or an oil based primer, but again if it has already been painted over it is likely that someone has already done this. If you paint right over wallpaper directly, there is a good chance that the water in the paint can reactivate the paste and actually start pulling the paper down or cause bubbles or cause seams to start seperating, etc.

I'm not a big texture guy so I hope someone else has ideas but here is what I might try. You can experiment with sand. Pour sand in the paint and roll it on, or apply with a big brush and make random swirls. I do this a lot of ceilings...hides small imperfections, but may be too rough for a wall surface that people touch or kids rub their face against. You can also try some Venetian plaster techniques....hides a lot, very random application. I have used some texture paint and this stuff will hide everything, but it is a very extreme texture that is too much for most people. I believe the stuff I used was made by Bondex. Of course, you can also do a knockdown or variation of by skim coating the entire surface and then knocking some of it down with a big drywall knife. Just some ideas.