I followed the instruction in reference manual to install aop in AS 4.0.5. Here is the exception I get upon starting the server:

14:13:59,859 INFO [Embedded] Catalina naming disabled
14:14:00,734 INFO [ClusterRuleSetFactory] Unable to find a cluster rule set in the classpath. Will load the default rule set.
14:14:00,734 INFO [ClusterRuleSetFactory] Unable to find a cluster rule set in the classpath. Will load the default rule set.
14:14:03,999 INFO [Http11BaseProtocol] Initializing Coyote HTTP/1.1 on http-0.0.0.0-8080
14:14:03,999 INFO [Catalina] Initialization processed in 3265 ms
14:14:03,999 INFO [StandardService] Starting service jboss.web
14:14:04,030 INFO [StandardEngine] Starting Servlet Engine: Apache Tomcat/5.5.20
14:14:04,358 INFO [StandardHost] XML validation disabled
14:14:04,780 INFO [Catalina] Server startup in 781 ms
14:14:05,155 ERROR [MainDeployer] Could not create deployment: file:/D:/tools/jboss-4.0.5.GA/server/all/deploy/httpha-invoker.sar/invoker.war/
java.lang.NoSuchMethodError: javassist.scopedpool.ScopedClassPool.<init>(Ljava/lang/ClassLoader;Ljavassist/ClassPool;Ljavassist/scopedpool/ScopedClassPoolRepository;Z)V
 at org.jboss.aop.classpool.AOPClassPool.<init>(AOPClassPool.java:66)
 at org.jboss.aop.classpool.AOPClassPool.<init>(AOPClassPool.java:56)
 at org.jboss.aop.deployment.JBossClassPoolFactory.create(JBossClassPoolFactory.java:67)
 at javassist.scopedpool.ScopedClassPoolRepositoryImpl.createScopedClassPool(ScopedClassPoolRepositoryImpl.java:99)
 at javassist.scopedpool.ScopedClassPoolRepositoryImpl.registerClassLoader(ScopedClassPoolRepositoryImpl.java:125)
 at javassist.scopedpool.ScopedClassPoolRepositoryImpl.findClassPool(ScopedClassPoolRepositoryImpl.java:106)
 at org.jboss.lang.AnnotationHelper.getCtClass(AnnotationHelper.java:111)
 at org.jboss.lang.AnnotationHelper.getAnnotationsInternal(AnnotationHelper.java:98)

Here is what I have done:
1. replace jboss-aop.deployer with jboss-aop-jdk50.deployer in /deploy directory.
2. enable Weaving to true
3. copy pluggable-instrument.jar in /bin
4. modify run.bat to add set JAVA_OPTS=%JAVA_OPTS% -Dprogram.name=%PROGNAME% -javaagent:pluggable-instrumentor.jar