I think what you may want to try is, as well as passing the variable in the html header, you'd want to put something like this in your object or embed tag for the .swf - <OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=4,0,0,0" ID=yourswf WIDTH=468 HEIGHT=300> <PARAM NAME=movie VALUE="[red]http://yourdomian/yourswf.swf?tld=tld[/red]"> ... ... </OBJECT>
Flash needs to be passed that variable directly when your browser calls for the movie to be loaded. It cannot grab something from the header string without it being called explicitly.
Hope this helps you out. And welcome to Webmaster World!