i've just set up tomcat 5.5.4 to work with xampp 1.4.11 in linux.
here's a brief overview of what i did:
1. installed xampp + xampp-devel
2. downloaded the latest jdk and installed to /opt/java. set the environment variable JAVA_HOME=/opt/java/jdk....
3. downloaded tomcat binary and installed to /opt/java/jakarta-tomcat-5.5.4
and set up a symbolic link to point it to /opt/java/tomcat
(at this point you can test if tomcat is working by starting up tomcat and pointing your browser to http://localhost:8080
4. downloaded jakarta-tomcat-connector-1.2.8 and compiled mod_jk.so
5. configured httpd.conf to load mod_jk.so and include mod_jk.conf
(you can follow this excellent howto i found on the net: http://johnturner.com/howto/apache-tomcat-howto.html
hope this helps