I expect (although am not sure) that calling new InititalContext() in tomcat will get you tomcat's context and not jboss's. You'll have to define a seperate paraterized context and use this for your lookup.
U will have to use the JBoss-Tomcat pair. Simply running JBoss and Tomcat will not let them talk to each other. The integration process is very involved. Thats y they provide u with the JBoss-Tomcat integrated bundle. Go in for that.