What you're doing is called "action chaining" and it's not recommended. If you want to pass parameters on to another action, you have to re-send the parameters in the query string. Example:
String url = "myAction.do?firstfield="+request.getParameter("firstfield"); return new ActionMapping(url, false);
A better alternative would be to use an ActionForm bean and have Struts automatically populate the properties of the bean rather than reading the parameters. The ActionForm does get passed on to a second action without jumping through hoops.