How can I pass a url variable through a flash file to another url?

Can anyone help me - I don’t anything about actionscript, but here is what I need to do:
I have a php page that is called with a variable username.
That php page plays a flash file that has a button to go to another php page.
I need that button to pass the username value to the url it is calling.

I have no problem passing the username variable to the flash file - I have tried both FlashVars and just including the value as part of the call to the flash file using php echo.

I just don’t know how to define the variable in the Action Scrip on (release) so the getUrl sends it along. The url that is called shows ?username = undefined.

PLEEEEAAASEE help - I’ve been pulling my hair out for days!

Thanks.