Hello,
If you use the typical code that adobe products create for displaying flash, they automatically include a line to detect if flash is installed, and if it is not, it takes the user to the page for downloading flash.
An example would be:
<object width="500" height="400" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0" classid="clsid

27CDB6E-AE6D-11cf-96B8-444553540000">
<param value="http://www.dnncreative.com/flashfile.swf" name="src"/>
<param value="False" name="CONTROLLER"/>
<param value="True" name="LOOP"/>
<param value="False" name="PLAY"/> <embed width="500" height="400" pluginspage="http://www.macromedia.com/go/getflashplayer" controller="False" loop="True" play="False" src="http://www.dnncreative.com/flashfile.swf"></embed> </object>