This is very easy to do using Ajax, using--for example--the Prototype framework of Script.aculo.us.
In a nutshell, I would set up a servlet to return whatever data is required for the table, based upon the user's combo-box selection, then use Ajax.Updater (from script.aculo.us) to get the data from the servlet and populate the table when the combo-box's onchange
This would provide the user with a dynamic application.
(Obviously, Ajax has nothing to do with JSP, per se)
Note: it is not good to store data in the Session that you could retrieve from a data store easily, because it limits the scalability of your application. Too many users = server runs out of memory