Running Tomcat

Tomcat is a free servlet/JSP container. The use of Tomcat on Windows does not need installation, so I just downloaded it and unpackaged it on the lab computer.
But there was a problem when start running the Tomcat server. When I ran the server using "startup.bat", there appeared an error saying " JAVA_HOME is not defined correctly, it should point to jdk instead to jre" and " the system cannot find file -Dsun.io.useCanonCaches=false". It was ridiculous for the server to give such an error message, because I was 100% sure that the variable was pointing to the JDK directory. So there must be any other missing in the environmental variable. Was it the CATALINA_HOME variable? I tried but it still didn't work.
Finally I found that the classpath variable was not defined in the windowXP system. I added this variable and made it point to the tool.jar in the jdk lib directory. And I found the tomcat server could be run.
So it's really important to check all the environment variables of jdk to make the tomcat work. But the error message in tomcat server is really misleading!