How can I JSP under Apache JServ?

Apache JServ is a servlet 2.0 compliant servlet engine, so the best you can do is the JSP 1.0 spec (you can't use JSP 1.1 as it requires servlet 2.2).

You can however add GNUJSP at http://klomp.org/gnujsp/. It supports JSP 1.1 on servlet 2.0 or 2.1 engines. In fact, in many ways it's a nicer environment to develop than Tomcat or JRun or other current JSP systems (good debugging and configurability). Unfortunately, the Servlet 2.2 features were too compelling and we had to move away from JServ and GNUJSP.