Well, not totally step by step, but some starting points:
1) Install Tomcat and make sure it response to port 8080.
2) Install jForum on Tomcat (either copy the war to the webapps directory or expand it manually in the webapps directory.
3) Run install program via the 8080 port and verify that jforum works.
4) Go to the tomcat connector's page and use this to get the IIS to TC JK 1.2 connector working.
http://tomcat.apache.org/connectors-doc/
FWIW, we use this as our production setup... it can be picky to get to work (mosting IIS's settings to get a the filter to work).
For extra credit, you might look at the IISConfig Listener class in the API.. this can be added to your server.xml file to automatically create the uriworkermap.properties file for ALL tomcat webapps (when server is started).
[originally posted on jforum.net by monroe]