Now as to your question:
If you are using a Model 2
pattern architecture for your app (and
you should), then the login form should submit to a
servlet that will authenticate the user and determine the user's role. (This info can be put into the session for future reference by subsequent requests).
Then, depending upon the determined role, you could forward to whichever JSP page is appropriate to display the UI for that role.
If the role UI's are not that different, I'd opt for creating custom tags that could be used on the page to conditionally include/exclude features not appropriate for the role (rather than having a lot of similar pages with only minor role-dependent differences).