Check out the JK Documentation for the Tomcat version you are using. It breaks down to several things. Installing mod_jk, configuring your workers.properties file and configuring your httd.conf file for Apache.
For Tomcat 4.1, the Minimalist
Doc is at
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/jk2/jk/aphowto.html