More often than not, the client wants to keep existing Flash assets when upgrading to SharePoint 2010. You will quickly find that the old work-around from SharePoint 2007 does not work anymore. Changing the “z-index” to a higher value does not bring the menu on top anymore.
The way to fix this issue in SharePoint 2010 is to modify the Flash container, and make it transparent. Add value=”transparent” to the object tag, and change the embed tag to paramname=”transparent”.