For Unix, the JAVA_HOME environment variable is what Tomcat uses to find
java.
If you're using 5.5 or higher, you can run tomcat without the full software development kit. If you're doing so, you need to set the JRE_HOME environment variable.
You can always set these right in the wrapper script (startup.sh) or write your own script that sets JAVA_HOME to what you want and then calls startup.sh.
[ September 22, 2005: Message edited by: Ben Souther ]