The only place where i know of where to put files is in the server/default/deploy direcory. This is valid for jboss3.0. Maybe you have to package your static html's in a war file, but i'm not sure.
If you would like to serve static html pages from jetty, you will need to add the following black to your jboss-service.xml file ($JBOSS_HOME/server/default/deploy/jbossweb.sar/META-INF/jboss-service.xml):
You will need to restart you Jboss instance for the changes to take effect. Please let me know if this helps.