These days I need to use the lightbox on some page with a flash banner. By default the flash banner is not hidden in Internet explorer because of some conflict with the z-index.
In the past I removed the flash content with JavaScript at the moment that the lightbox was activated, but this is a really workaround.
After a search on Google I found this information on the adobe website:
wmode - Possible values: window, opaque, transparent. Sets the Window Mode property of the Flash movie for transparency, layering, and positioning in the browser.
- window - movie plays in its own rectangular window on a web page.
- opaque - the movie hides everything on the page behind it.
- transparent - the background of the HTML page shows through all transparent portions of the movie, this may slow animation performance.
The "wmode" option is teh magic, I think by default "window" is used.
I think every webmaster should use the SWFobject to show flash within a website:
<script type="text/javascript" src="swfobject.js"></script>
<div id="flashcontent">
You need to enable flash...
</div>
<script type="text/javascript">
var so = new SWFObject("movie.swf", "mymovie", "468", "60", "8", "#FFFFFF");
so.addParam("wmode", "opaque");
so.write("flashcontent");
</script>