TIP - To keep your main (html) - page neat and easy to read, you can put the head or body javascript into an external .js file (minus html tags) and reference it from your page thus -
<script language="JavaScript1.2" src="MY.js"type="text/javascript"></script>

Right-click - 'select all' (ctrl-a) then copy (ctrl-c) and paste to 'BODY' of your page.

There are in total four variables you'll need to configure- the width, height, speed, and contents of the marquee. Please refer to documentation inside the script for instructions.