This forum is intended for questions and comments about this web site, www.javaranch.com. It is not for questions about the Java language - that's what all our other forums are for. Specifically, this sounds like it would be more appropriate on the Servlets and JSP's form, so I'm moving it there.
There are so many other things that could be 'wrong' besides JRun. I've heard many people rave about JRun vs. Tomcat. Myself, I like Tomcat.
Have you checked: -What else is the machine running? -Is some other program causing a memory drain? -How old is the install of WinNT (OS's get cluttered after several months). -What service pack? -have you tried Apache Web Server, as opposed to IIS. -Have you configured JRun as a 'production' system, as opposed to a 'development' system.