sizing?
Sizing A liquid mixture that is applied to the wall prior to wallpaper installation. Sizing creates a uniform porosity on the surface of your wall and increases the tack of the wallpaper during installation. Sizing should not be mistaken for a primer/sealer (see "primer/sealer" above).
Primer/Sealer An alkyd or acrylic-based liquid applied to the wall prior to wallpaper installation. Primer/sealers soak into a porous wall surface much like sizing (see "sizing" below). However, Acrylic-based primer/sealers also soak into latex paint and re-bond the paint to the wall. This is important because most wallpapers expand when wet, as they dry they tighten to the wall. Poor latex paint will pull away from the wall during this drying stage.
http://www.wallpaperstore.com/WallpaperTerms.htmZinnser makes several products that should help, you should be able to find it at a home center or paint store.
Just a couple of their products:
Z-54™ Heavy-Duty Wallcovering Primer with tack is a fast-drying water-based primer that dries to a clear, tacky film. It adheres to all difficult-to-hang surfaces such as gloss paint or existing vinyl's or foils without sanding. It can be used under any type wallcovering.
SHIELDZ CLEAR adheres to all sound surfaces including hard-to-stick surfaces such as glossy paint, ceramic tile, glass, Formica®, and vinyl wallcovering. No sanding is required.
http://www.zinsser.com/subcat.asp?CategoryID=2And as I_Make_Mistakes stated, prime or size after sanding
Good Luck