var hostPageUrl:String = ExternalInterface.call("window.location.href.toString");
var queryString:String = ExternalInterface.call("window.location.search.toString");
This will give you something like "?param=value&foo=bar..." What about the referrer of that page? 2EZ:
Of course the key to all of this is script access. The SWF needs to have it. If the SWF is from the same domain as the web page, it gets this by default. If not, then you need to set allowScriptAccess="always". That gives the SWF the keys to the kingdom, if you will. Of course you could use an IFrame for the SWF and sandbox it in.