Yo utilizo este codigo en mi pagina para detectar si el navegador soporta flash o no. Si lo soporta cargo un fichero swf y si no un banner que es un gif.
<object id="arranque" codebase="http://active.macromedia.com/flash2/cabs/swflash.cab#version=2,0,0,0" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="280" height="40">
<param NAME="movie" VALUE="banner0.swf">
<param NAME="quality" VALUE="high">
<script LANGUAGE="JavaScript">
<!--var ShockMode = 0;
if (navigator.mimeTypes && navigator.mimeTypes["application/x-shockwave-flash"] &&
navigator.mimeTypes["application/x-shockwave-flash"].enabledPlugin) { if
(navigator.plugins && (navigator.plugins["Shockwave Flash"] ||
navigator.plugins["Shockwave Flash 2.0"])) ShockMode = 1;}function
checkForShockwave(){ navigator.plugins.refresh(); if (
navigator.plugins["Shockwave Flash"] || navigator.plugins["Shockwave Flash 2.0"]
){ parent.location.reload(); } else { setTimeout( "checkForShockwave()", 1000
); }}if (!ShockMode && navigator.appName &&
navigator.appName.indexOf("Netscape") != - 1 &&
navigator.appVersion.indexOf("4.") != - 1&& navigator.javaEnabled() &&
netscape.softupdate.Trigger.UpdateEnabled() &&
document.cookie.indexOf("StartedShockwaveInstall") == -1) { var jarPath = new
String(""); if (navigator.platform.indexOf("Win32") >= 0 ) jarPath =
"http://download.macromedia.com/pub/shockwave/jars/english/silentflash32.jar"
else if (navigator.platform.indexOf("Win16") >= 0 ) jarPath =
"http://download.macromedia.com/pub/shockwave/jars/english/silentflash16.jar"
else if (navigator.platform.indexOf("MacPPC") >= 0 ) jarPath =
"http://download.macromedia.com/pub/shockwave/jars/english/silentflashppc.jar"
if (jarPath.length) { netscape.softupdate.Trigger.StartSoftwareUpdate
(jarPath, netscape.softupdate.Trigger.FORCE_MODE);
document.cookie='StartedShockwaveInstall;path=/;'
setTimeout("checkForShockwave()", 1000); }}
if ( ShockMode ) {
document.write('<EMBED SRC="banner0.swf"');
document.write('swLiveConnect=FALSE WIDTH=300 HEIGHT=50');
document.write(' QUALITY=high BGCOLOR=#FFFFFF');
document.write(' TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash">');
document.write('</EMBED>');
} else {
if (!(navigator.appName && navigator.appName.indexOf("Netscape")>=0 && navigator.appVersion.indexOf("2.")>=0)){
document.write('<img border="0" src="banner.jpg" WIDTH="242" HEIGHT="51">');
}
}//-->
</script>
<noembed>
<img border="0" src="banner.jpg" WIDTH="242" HEIGHT="51"></noembed><>
<img border="0" src="banner.jpg" WIDTH="242" HEIGHT="51"></></object>
O carga el fichero banner0.swf o banner.jpg