Well, I have seen it done, and I'm sure it was with Javascript. Just keep searching these kinds of sites and you might get lucky.
Depending on what this marquee is for, there may be another method. If you have a decent photo-editing package installed, you may have a GIF animator, and you might be able to get a similar effect. Ditto for Flash files, though they generally need more advanced software to make.
This method may be just what you want (if this is for a heading or other permenant feature) or it may be totally useless (if it needs to be updated every day).