Anyone who has ever mixed DHTML and flash will know that flash elements have a very nasty habit of showing up on top no matter what.
DHTML layers that should float over your flash element end up floating behind it and in general this can really mess up your site.
Well thats not strictly true anymore.
Ever since flash 6 it has been possible to modify how your flash player is displayed using the window mode "wmode"
there are 3 wmode values
wmode=windows
(which is the default so you dont need to put it in)
wmode=opaque
which sets your flash object to act like any other page element, so you can float DHTML and javascript layers over it without the flash movie showing through
and
wmode=transparent
Which makes the background of the page, or the DHTML layer underneath the Flash movie or layer, to show through all the transparent portions of the movie.
To change the mode you need to edit in 2 places
In the Object tag, add the following parameter (opaque is shown as an example):
<param name="wmode" value="opaque">
and in the Embed tag, add the following attribute:
wmode="opaque"