Whenever I’m confused about the wmode parameter when embedding Flash objects into websites I turn to http://www.communitymx.com/content/article.cfm?cid=e5141. It describes the three modes “window”, “opaque”, and “transparent” with just the right degree of details and contains sensible demos. Of course, it’s helpful that the explanations are also related to DHTML menus because problems with those most often rise questions about Flash’s wmode parameter.