${expr} in jsp requires two things
1 - A JSP2.0 container - eg Tomcat 5. In a JSP1.2 container you can only use EL in the JSTL tags.
2 - Your web.xml file must declare itself as being version 2.4
http://forum.java.sun.com/thread.jspa?threadID=629437&tstart=0
reply 6
In a JSP2.0 container, ${expr} is a runtime expression.
if you use tomcat 5, and declare your web.xml as version 2.4, you can use ${expr} anywhere that you can use <%= expr %>
So you can use it anywhere in template text, and also as an attribute to any tag that takes a runtime expression.