Registering your copy has nothing to do with creating HTML pop-ups for the game. However, it does tell us that you have a legitimate copy with a correct serial number - it costs you nothing to register. Once you have registered you will find that other users (myself included) will be far more willing to help you with your questions and problems.
There is a lot more to creating HTML pop-ups than your description - it is not as simple in Trainz as it is with normal web pages. I would NOT use Dreamweaver to create the HTML pages as the code it normally creates will cause you problems in Trainz.