How do I pass information to the .swf via the param or embed tag?

I have a flash movie that tries to load an XML file on startup. Right now it looks for a hard-coded filename, but I’d really, really love to be able to pass a filename in through the webpage that plays it. (possibly through a param tag or some such?) I’ve seen hints of how to do this on the forum, but can’t find any mention of it in the help files. How can a webpage send data in to a flash movie?

Thanks!