Creating an overlay in flash

Hi,

Can anyone help me understand how we can create an overlay in flash?

I am very new to flash and I want a case where user clicks something in the flash file, I want to check if he is logged in, if he is not then give him a login screen on top of whatever he was viewing in the flash file. Once the login screen is displayed, he should not be able to do anything in the background - only when the login credentials are verified, will he be able to do anything behind this overlay.

I don’t want to go to a different frame, I want to show a screen on top of the current screen being viewed by the user.

Any thoughts?

Thanks in advance,
Mandy.