Installing Apache Tomcat 6 on Mac OS X is primarily a matter of downloading the appropriate packages and then following the UNIX installation instructions included with the package. However, OS X does have some peculiarities that make installation somewhat different than on your average UNIX box. These instructions will work with OS X 10.6 Snow Leopard and Java 6, but I have not verified it myself. I have also seen individuals using these instructions to get up and running on OS X 10.4 Tiger, but again I don't have the time to verify that everything works myself.