What you are asking for, cannot be accomplished in Flash. It requires database manipulation and management, so it is only feasible using php/MySQL in combination with html for the visual part.

Have a look here where you can see an example of a login script

__________________
Navaldesign
Logger Lite: Low Cost, Customizable, multifeatured Login script
Instant Download Cart: a Powerfull, Customized, in site, DB driven, e-products Cart
DBTechnosystems.com Forms, Databases, Shopping Carts, Instant Download Carts, Loggin Systems and more....
Advanced BlueVoda Form Processor : No coding form processor! Just install and use! Now with built in CAPTCHA!