Hi Mitch: The most important consideration is how flat the cast top is. To measure this, I would put a 120 grit sanding disk on my 7" angle head grinder and sand off the bulk of the rust. Then I would work in a 10% mixture of oxalic acid (naval jelly) and scrub off with warm water and a bristle brush, then dry completely. I then use a straight edge (level, drywall cutting T, etc), lay it across the table on edge and see if you can get a .001 inch or greater feeler gauge under the straight edge. In my experience, any warp greater than .004-.005 or any large rust pits means that you will need to take the top to a machine shop to have them surface grind it flat.
You will probably also have to have the pillow block bearings that hold the blade shaft replaced. Inactivity is what usually gets those things. If you have to take it to a machine shop, they should be able to replace the bearings also.
For more info, there is often a lot of table saw restoration discussion at http://www.wwforum.com/