How do I configure IPlanet 4.0 (web server) to work with Tomcat?
Just run with one or the other. They will both do the same job!
We have just moved from tomcat to iPlanet 4.1 for our prod environment and now do not use TC at all.
[Well, one reason might be that Tomcat may support a more recent version of the spec, or that iPlanet may have bugs that Tomcat does not... But at the moment, they both allegedly support version 2.2 of the Servlet spec. See What version of the Servlets or JSP specification is supported by my favorite servlet product? -Alex]