These are WARNings not ERRORs, so they mean that everything should still run. That is not to say that you shouldn't try to clean them up if you are able. Are you unable to start the server or display the app?
If you are just starting with JBoss, why are you using 4.2.3?
Are you using any Spring in your app? These warnings are related to log4j, maybe you should post this question on the main JBoss forum, you will get a lot more traffic there.
Please let me know.