You need a JDK 1.4.x installed to run Tomcat.
Also, the environment variable JAVA_HOME must be set correctly.
It should point to where Java 1.4.x is installed.
On Mac OS X & other unix-based systems:
set JAVA_HOME=/usr
On some unix systems, you need to point to where it is installed. For example:
set JAVA_HOME=/opt/j2sdk1.4.2
On windows, point to where you installed the JDK:
set JAVA_HOME=c:\Program Files\Java1.4\