While Matt was talking about the Tomcat Service Manager, coincidentally, I was trying to install Tomcat 4 as a service on a Windows 2000 machine yesterday. For various reasons, I didn't want to install Tomcat via the .exe and therefore had to hunt around for the command line that installs the NT service. For (my) future reference, here it is, split over several lines for readability.

set JAVA_HOME=c:\j2sdk1.4.2_01
set CATALINA_HOME=c:\jakarta-tomcat-4.1.27

%CATALINA_HOME%\bin\tomcat -install "Jakarta Tomcat 4"
  %JAVA_HOME%\jre\bin\server\jvm.dll
  -Djava.class.path=%CATALINA_HOME%\bin\bootstrap.jar;%JAVA_HOME%\lib\tools.jar
  -Dcatalina.home=%CATALINA_HOME% %CATALINA_OPTS% -Xrs
  -start org.apache.catalina.startup.Bootstrap -params start
  -stop org.apache.catalina.startup.Bootstrap -params stop
  -out %CATALINA_HOME%\logs\stdout.log
  -err %CATALINA_HOME%\logs\stderr.log