Some services require the running of a command, script, or batch file to uninstall them. For example, to uninstall Tomcat as a Windows service you have to run the command service.bat remove located in the \bin directory, where is the home directory of the Tomcat install, e.g. C:\Program Files\Apache Software Foundation\Tomcat 5.5. I have a Tomcat IA installer project and I run this command in the pre-uninstall section of the Advanced designer as part of an "Execute script/batch file" action. Hope this helps you.
Once you register a window service using the action "Register Window Service" then during uninstall IA will automatically remove the service for you. If you want to execute custom script for uninstalling then you need to provide an action to run a batch file or script.
