Here's a kewl tutorial on Portlets, Portlet Forms, Portlet JSPs, and Linking back to the Portal. I'm not sure if you're old JetSpeed or JSR-168, but either way, the concepts are pretty much the same:
http://www.technicalfacilitation.com/get.php?link=portleturi A big difference is PortletURI for Jetspeed, PortletURL for JSR-168
Maybe this code snipped will give you a few ideas:.
<%
PortletURL url = response.createActionURL();
url.setParameter("shift", "true");
%>
public void processAction...
if (request.getParameter("shift") != null) {
}
....
Good luck, dude. Happy Portal!