为什么WebWork上手会有这么多问题呢？

今天写《webwork in aciton》中的helloworld又出现了问题，和上次的问题是一个类型的，都是找不到类具体错误信息：
javax.servlet.ServletException: Wrapper cannot find servlet class com.opensymphony.dispatcher.ServletDispatcher or a class it depends on
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
java.lang.Thread.run(Thread.java:595)


root cause

java.lang.ClassNotFoundException: com.opensymphony.dispatcher.ServletDispatcher
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1340)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1189)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
java.lang.Thread.run(Thread.java:595)

类都存在，为什么就是找不到呢？两天都没弄出个能跑的程序，唉！
环境 europa eclipse3.2.2＋tomcat5.5.17  webwork的jar是2.2.6的