are you using the JBossIDE-Plugin for Eclipse?
It contains a nice tutorial showing you how to debug your project using Eclipse.
You can download the JBossIDE and the tutorials from sourceforge.
Unfortunately, you do not have the same available deployment methods as per standalone Tomcat. You can change the context with a jboss-web.xml element. You can also modify the work directory by defining your own Jasper instance per web.xml. There is a thread for this although it is not very elegant.
I would however, suggest looking at the Lomboz-Eclipse plugin for JBoss and view Vashistvishal's tutorial for JBoss - see the Beginner's forum.
Thank your help!
I found another way to debug JSP in Eclipse with Lomboz plug-in! That is import the tomcat-4.1.x\work\MainEngine\localhost\debugJSP dir into the J2EE project's j2src dir. Done! Simple!