If you're planning on stripping your old wallpaper prior to having your room painted or new wallcovering hung, I'd like to warn you ahead of time that wallpaper stripping is not for the faint of heart. It takes patience, and it's often tedious. And depending on how the wall was prepped before the old paper was hung, it can also be difficult. I've periodically run into homes where wallpaper was installed over new drywall without the walls being primed first. The result? The top layer of the drywall comes off the with paper. That means a wall repair before moving on - an additional expense.
So I've given my warning, but some of you may want to forge ahead anyway. In that case, I would suggest you check out this video from This Old House on How to Strip Wallpaper. (If after you've reviewed this you're having second thoughts, I'd like to point out that stripping old paper is going to be the least expensive part of wallpaper hanger's bid. You may want to get an estimate to see what it's going to cost to have a pro do it, and then evaluate whether the hassle is really worth it for you.)