It’s a cakewalk, you can simply use the <object> tag or a javascript called SWFObject.
The SWFObject also get rid of the annoying IE7 “press space bar or enter to activate and use this control” that appears on embedded flash.
You can get SWFObject here: https://blog.deconcept.com/swfobject/
just add the jacascript call to your header. If you need help with it just ask.
After that simply add the following code just below <div id=”header”>
<script type="text/javascript" src="swfobject.js"></script>
<div id="flashcontent">
This text is replaced by the Flash movie.
</div>
<script type="text/javascript">
var so = new SWFObject("https://yourswflocation/header.swf", "mymovie", "860", "180", "8", "#000000");
so.write("flashcontent");
</script>
otherwise, without the SWFObject javascript as follow:
<OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
codebase="https://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0"
WIDTH="860" HEIGHT="180" id="swfheader"><PARAM NAME=movie VALUE="https://yourswflocation/header.swf"><PARAM NAME=quality VALUE=high><PARAM NAME=bgcolor VALUE=#FFFFFF><EMBED src="https://yourswflocation/header.swf" quality=high bgcolor=#FFFFFF WIDTH="860" HEIGHT="180"
NAME="swfheader" ALIGN="" TYPE="application/x-shockwave-flash"
PLUGINSPAGE="https://www.macromedia.com/go/getflashplayer"></EMBED></OBJECT>
Adjust the swf path to your needs.
Hope this helps