Adding a marquee may be either a great or a terrible addition to a site. First of all, too many marquees or poorly placed ones is very bad for a site. Marquees are creative and a simple way to have sort of a ticker on your site. I have it on my homepage and it shows the current updates. It is supptle way to emphasize a certain aspect of your site. Below is a demonstration of a marquee with 350 width, made just by adding width="350" inside the marquee tag.
Here the marquee is rotating horizontaly but it can rotate vertically as well. It is just text enclosed in marquee tags. Instead of the "p" tag "marquee" is put. Below the marquee rotates upwards and has a height of 50. Those two things are added by adding a height="50" and direction="up" inside that marquee tags.
Be discrete when using marquees as they may look good to some but very annoying to others. The speed of the marquee can also be regulated but I am not sure now how to do it. I am looking for that property.If you are interested in more details about marquees, then mail me and I will give you more information.
I am not really sure what it does but I think that it is a good idea to add a loop="infinite" inside the marquee tag as well as a behavior="scroll" part. I am looking for other "behaviors" of marquees.
You can also add a onmouseover="this.stop()" and onmouseout="this.start()" parts as well, if you want your marquee to stop when the mouse is over the text.