I couldn't find a great way to do an iframe in an xhtml site and still maintain accessibility - until I came across malsup's media plugins. They basically create a link to the swf, mp3, or quicktime and replace the link with the content via a custom class on the href tag.
Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded. It lets you attach events to any alements in the page without directly interfering with the mark-up; all those annoying onload, onclick and onwhatever stuff isn’t needed anymore; just write it in here. An example with created-on-the-spot functions, which keeps everything very compact and quite understandable, could be