I have taken down lots of wallpaper and I have never used a steamer although I have heard that it does work. The cost and hassle of renting the steamer from Home Depot has always precluded me from using a steamer. Diff with very hot water has always worked for me. Some steps you might want to take:
1. Score the walls with a razor blade. You don't need one of those scoring tools that they sell for 6 bucks, a razor blade will do. Ensure that you make Xs on the wall that cut the paper but do not push down so much that you cut into the wall.
2. Use Diff in the proper ratio with hot water and a sponge or roller. Roll or sponge the walls several times. Let it soak in for 10 minutes or so. The more you soak the walls the easier the paper will be to take off. If the paper was put up well and you soak it thoroughly, the paper will fall off with minimal effort. If the paper was put on poorly it will be a fight no matter what you do.
3. Scrape the paper off with a scraper that you find in the paint section of the store.
4. Once you remove all of the paper rinse the walls with water and a clean sponge and let it dry.
5. There will probably be spots that you need to spackle. You will need to spackle those with some joint compound and sand them when they dry. I prefer to hand sand because you get a much better feel for the smoothness of the spot. If you sand it well, when you paint, the spots you spackled will not show at all.
6. Once you sand the wall you will again have to rinse the wall with a slightly damp rag so that the dust from the sanding is removed. You do not want to rinse the wall too hard so you do not remove the dry spackle.
7. Once the wall has dried and you have taped the trim, you are ready to paint.
Hope this helped.