It looks like a simple procedure but many times it's a problem to insert a flash file as website's header. Sometimes it looks great with some browsers and doesn't show at all with others. This code was tested to work by many webmasters and by myself in the most of the browsers.

Simply adjust the width, height and the URL of the swf file in both, object and embed instructions

<object
  classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
  style="display:block"
  codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab"
  width="200"
  height="100">
  <param name="movie" value="http://www.my_site.com/path/to/file.swf">
  <param name="quality" value="high">
  <param name="menu" value="false">
  <embed
    src="http://www.my_site.com/path/to/file.swf"
    menu="false"
    quality="high"
    pluginspage="http://www.macromedia.com/go/getflashplayer"
    type="application/x-shockwave-flash"
    width="200"
    height="100">
  </embed>
</object>