Remove the wallpaper before painting. It may take a lot of work, but the end product will be much better.
My Mom's house has wallpaper that's been painted over and I don't think it's attractive at all. Also, they tried removing it and found that once wallpaper has been painted it's nearly impossible to remove.
We bought a chemical stripper (available in the wallpaper department) to help with wallpaper borders around our house.