I assume that by "Wallboard" you mean the type of paneling that has a vinyl finish that looks like wallpaper? Or do you mean drywall drywall that has been wallpapered?
If the latter is the case, I strongly reccomend that you remove the existing wallcoverings before you hang the new one.
If the former is the case, then yoiur in for a project. Most of these types of paneling have joint strips that cover the seams between each panel. Looking at the profile of these strips, they resemble the letter "H". These should be cut away with a sharp razor knife (I reccomend the Tajima 650 for this. Can be found at Sears). Then the surface must be washed with a stron cleaner and allowed to dry overnight. Then sand the surface lightly with 150 grit sandpaper, and apply a coat of Brunning's "Grabber Plus" adhesion primer. Then the joints where the strip was removed have to be treated as a seam in drywall would be treated, filled, taped and feathered. Now that you have a smooth surface, apply a coat of "Ultra Prime, Pro-977", marketed by Roman Adhesives. This is a primer meant for wallcoverings, it's wonderful stuff. When your done papering, keep in mind that it will take a long time for the paper to dry, it could be as much as a week or more. During this time, the paper will be delicate and easily damaged. You will also notice small bubbles, about the size of a 50 cent coin, this is normal and as long as you can move them around, they should go away as the paper dries.