I\'m currently using jQuery, as well as swfObject to dynamically embed the swf movie into my web page.
I currently having a problem on embeding immem\'s music player
Note, you'll need wmode=transparent if you intend to obscure flash with an image or html things
Typically the easiest thing to do is plain ol' <body onload="..."
which would wait for your external resources to finish loading before calling your handler.
However, if you're using swfObject to add an embedded plugin dynamically the browser will fire the onload for the body exclusive of your flash movie (it doesn't know anything about your plugin).
See http://blog.deconcept.com/swfobject/forum/discussion/271/javascript-onload-event-does-not-reflect-page-load-using-swfobject/ for a similar discussion to yours. It's my best guess that you cannot do what you want without modifying the original swf in some fashion.
You could do this from within the flash movie. However then you will need to have control over the movie (which you may not have).
Problem with the above-mentioned solution of using window.load() is it is not useful if your main swf weights only 1 kb but it actually doesn't display anything (just being a container that gets additional content loaded, which is often the case in flash files.
What i would do is use Actionscript 's ExternalInterface class that allows your flash player to communicate with the javascript functions available in the html file which contains the flash file. You could have your flash file call a javascript function that triggers a function that tells your javascript processing script that the flash is ready. What is nice with this is that you get the exact level of control you need over what should be loaded in the flash file when the javascript takes over.
See this for more info on the use of ExternalInterface: http://blog.circlecube.com/2008/02/01/actionscript-javascript-communication/