use macromedias new guidelines for flash movies, they are garaunteed to work, and you don't need js plugin detection... it doesnt detect half the mac browsers and unix browsers anyway...
use this:
<object type="application/x-shockwave-flash" data=".." width="xxx" height="xxx">
<param name="movie" value="..." />
<param name="menu" value="false" />
<param name="quality" value="high" />
<param name="bgcolor" value="#" />
<!--- put your alternate content here --->
</object>
hope this helps
regards, seb