I double-checked the file and it does contain the com/javaranch/common directory.
Correct, I am using OS X with Java 1.5.
I've found that if I reverse the order of the jar files - typing:
$ javac -cp ~/tomcat/apache-tomcat-6.0.20/lib/jr.jar:~/tomcat/apache-tomcat-6.0.20/lib/servlet-api.jar -d classes src/***.java - it returns errors regarding the javax.servlet classes; so whatever comes second in that classpath list doesn't work.