Unpack the tomcat distribution:
unzip jakarta-tomcat-5.0.19.zip
Make sure that 'JAVA_HOME' is set in your environment.
Open up a shell and start tomcat:
On Unix or Mac OS X:
cd jakarta-tomcat-5.0.19/bin ./startup.sh
On Windows
cd jakarta-tomcat-5.0.19/bin startup
Note: On Unix or Mac OS X you may need to make the scripts executable first:
cd jakarta-tomcat-5.0.19/bin chmod u+x *.sh
Check to see if it running at http://localhost:8080