When starting Tomcat l get "java.lang.NoClassDefFoundError: org/apache/tomcat/startup/Tomcat"
You are missing the webserver.jar from your classpath. The start script on unix dynamically builds your classpath, including all the files in the server's lib directory. On Windows, you have to manually edit this, although it should have webserver.jar included out of the box.
Try editing the tomcat.bat or tomcat.sh in your bin directory. This bat/script file is referenced by virtuall all scripts in this directory. You can see if it's properly finding the TOMCAT_HOME environment variable, and if it's properly defining your classpath.