How to detect browser no flash give alternate with gif

Let see, we have one file .swf and one file .gif and we want display the flash file first, and if the browser doesn't support, it will display the .gif version.
Here is the code.

JAVASCRIPT CODE:
<br /><object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://active.macromedia.com/flash/cabs/swflash.cab#version=3,0,0,11" name="sw" id="sw" height="164" width="165"><br /><param name="movie" value="file.swf"><br /><param name="quality" value="high"><br /><param name="Loop" value="true"><br /><param name="play" value="true"><br /><param name="wmode" value="opaque"><br /><param name="allowScriptAccess" value="sameDomain"><br /><param name="bgcolor" value="#000000"><br /><br /><!-- begin the JavaScript --><br /><script language="JavaScript"><br /><br />//If this browser understands the mimeTypes property and recognizes the MIME Type //"application/x-shockwave-flash"...<br />if (navigator.mimeTypes && navigator.mimeTypes["application/x-shockwave-flash"]){<br /><br /> //...write out the following <EMBED> tag into the document.<br /> document.write('<embed src="file.swf" quality="high" bgcolor="#000000" width="165" height="164" name="pmi_flash" align="middle" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" LOOP="true" PLAY="true" wmode="opaque" />');<br />}<br /><br />//Otherwise,...<br />else {<br /><br /> //...write out the following <IMG> tag into the document. The image need<br /> //not be the same size as the Flash Player movie, but it may help you lay out the<br /> //page if you can predict the size of the object reliably.<br /> document.write('<IMG SRC="file.gif" >');<br />}<br /><br /><br /></script><embed src="file.swf" quality="high" bgcolor="#000000" name="pmi_flash" allowscriptaccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" loop="true" play="true" wmode="opaque" align="middle" height="164" width="165"><br /><br /><!-- Close the OBJECT tag. --> <br /></object><br />