Simple version that works, and validates, without having to use all that horrible flash code you normally see:
<object type="application/x-shockwave-flash" data="images/intro.swf" width="518" height="255" id="flash">
<param name="movie" value="images/intro.swf" />
</object>
In the data section (and the value section in the param tag), type where it can find you flash movie and it's name. Adjust the width and height to your flash movie's width and height, and you're golden.