I've been told that the crossdomain.xml policy file is available to the flash 6 player but had no luck when testing it.

Here's a test exercise...
http://www.mixart.com/xmltest.zip

Included in the zip is an FLA and the 2 xml files (the one to be loaded and the crossdomain.xml).
Publish the SWF and place it on your own server and see if it loads with Flash Player 6 installed. No dice for me.
Here are the XML files linked to from the FLA...
http://www.mixart.com/jobs.xml
http://www.mixart.com/crossdomain.xml

If anyone can get it working, let me know the secret.

Thanks / Mick