Hi, Kim. This is pretty specialized work and I would suggest that you post your question at http://www.oldhouseforums.net/index1.html . You should be able to just cut and paste the address. Then look for the link to the drywall/plaster forum.
We have both put drywall over the old cracked plaster and restored some walls by painting on a binder and applying fiberglass cloth at my daughter's old house. Part of this decision, I think, depends on the amount of problems areas. They guys at that board tend to usually want to repair the plaster rather than use those methods. You might want to let them know the age of the house and a rough idea of the size of the problem areas.