Looks like jboss was not installed properly. The class that is missing (i.e. ServerImpl) should present in the C:\Program Files\JBoss\jboss-4.0.4.GA\lib\jboss-system.jar file. Doing a proper reinstall of jboss should solve this issue
Thx, jaikiran. I took you're advise and re-installed but this time using the web installer and works fine. Previously I just downloaded and unzipped all of the files...either something went wrong with the download or the zip compressed file was missing a few libraries.