Ciao,

prova questo

codice:
bann = new Array()
ran = Math.floor(4 * Math.random());

bann[0] = '<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0" width="468" height="60">'+
'<param name="movie" value="banner.swf">'+
'<param name="quality" value="high">'+
'<param name="bgcolor" value="#ffffff">'+
'<embed src="banner.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" bgcolor="#ffffff" type="application/x-shockwave-flash" wmode="transparent" width="468" height="60">'+
'</embed>'+
'</object>'

bann[1] = '<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0" width="468" height="60">'+
'<param name="movie" value="banner1.swf">'+
'<param name="quality" value="high">'+
'<param name="wmode" value="transparent">'+
'<embed src="banner1.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" bgcolor="#ffffff" type="application/x-shockwave-flash" wmode="transparent" width="468" height="60">'+
'</embed>'+
'</object>'

bann[2] = ''
..............
..............

bann[3] = ''
..............
..............
document.write(bann[ran]);
Copia il codice per il caricamento casuale del .sfw e mettilo in un file esterno .js

poi lo richiami con <script type="text/javascript" crc="tuo_file.ja"></script>

e lo metti nel punto dove vuoi caricare il banner.

M.