Have you tired creating a trigger and it isn't working or are you looking for someone to provide you a complete trigger? These forums are usually to help people with problems they are having and not providing complete works.

First off do you use stored procedures to insert the data into the Users table? If so, can you add your logic there instead of adding a trigger? I would recommend this approach to using a trigger if you can help it.

If it has to be done using a trigger (you will know this better than I) what are your specific questions about creating the trigger?