Pass Parameter from JS to Flex and Flex to JS

Flex & Javascript Basics - Using ExternalInterface
http://www.switchonthecode.com/tutorials/flex-javascript-basics-using-externalinterface

Passing variables to Flex in the embed page (or URL string)
http://thanksmister.com/index.php/archive/passing-variables-on-the-url-string-to-flex-2/

Pass parameter to Flex in SWFObject
http://code.google.com/p/swfobject/wiki/documentation