Below code will helpful to create popup in liferay :
In Liferay 5 :
<portlet:renderURL var="somePageURL" windowState="<%= LiferayWindowState.POP_UP.toString() %>"> <portlet:param name="jspPage" value="/jsp/some/page.jsp"/> <portlet:param name="redirect" value="<%= currentURL %>"/> </portlet:renderURL>