Well, I just installed the latest version of More_Pics. I didn't know there was a version without the pretty lightbox ;).
But anyway, I fixed the problem. This is how the swf file is included now (bold parts fixed the problem!!):
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0"
width="986" height="200" hspace="0" vspace="0">
<param name="movie" value="images/header.swf">
<param name="quality" value="high">
<param name="wmode" value="transparent" />
<embed src="images/header.swf" wmode="transparent" width="986" height="200" hspace="0" vspace="0" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash"></embed>
</object>
The first one (param) is for IE and the embed attribute works for Mozilla. Looks pretty good now in all browsers.
Thx for your help.
Sebastian