What you're doing is a static include. A static include is resolved at compile time, and may thus not use a parameter value, which is only known at execution time.
What you need is a dynamic include:
<jsp:include page="..." />
Note that you should use the JSP EL rather than scriptlets. It also seems that you're implementing a central controller with index.jsp. You should use a servlet to do that instead, and dispatch to the appropriate JSP from this servlet. Or better, use an existing MVC framework like Stripes or Spring MVC.