hello...
that is a non-standard tag that you shouldn't probably use - microsoft invented it years ago, and other browsers support it to be nice...
http://en.wikipedia.org/wiki/Marquee_tag
there is a proposed css spec for it, but for now you should use a javascript equivalent or the likes, i think...
(especially if you want valid html, as it won't ever pass those tests as it's not a valid tag)
sitruc