The Flash movie above combines plug-in detection and preloading.
If the browser doesn't have any Flash plug-in, then it will be redirected to another page via JavaScript.

If the plug-in is earlier than version 6, the embedded .swf redirects the browser to that same page, i.e., noflash5.htm. It does this by using a form of ActionScript that earlier versions of Flash will ignore, i.e., a "with" statement:

switch (true) {
    gotoAndPlay (3);
}

How did I make this html page?
Dreamweaver 4.
I used the built-in "check for plug-in" behavior.
If you view the source of this page to see the code, note that there are scripts in three places: the head of the document, in the body tag, and at the bottom of the document.

SEE ALSO:
Flash can also publish your .swf with an HTML template that includes Plug-in detection.
MENU || File >> Publish Settings >> HTML >> Template >> User Choice