The registration feature is required to have the following properties:
It is to collect the user's first name, last name, user name, and password.
All fields are required, and user names and passwords must be at least five characters each.
The user should be able to cancel the registration process at any point before submitting it. When registration is canceled, the user should be taken back to the main posts page.
The submit and cancel buttons should be disabled while the registration is in progress to prevent the user taking an action while registration is in progress.
If an account with the supplied user name and password already exists, the user should be notified of it.
If registration is successful, the registration form should be cleared and the user should be notified.
If registration fails, the form should remain populated and the user should be notified that something went wrong.
Collecting the user data is simply a matter of creating a form that collects the information and submits that data to the registration service.
To meet the requirements of making the form fields mandatory and enforcing the length requirement for the user name and password, you will use the built-in Flex Validation classes: (http://livedocs.adobe.com/flex/3/html/help.html?content=validators_2.html).
You can enable cancellation simply by providing a cancel button that returns the user to the main posts view.
Notifying the user about the status (pass, fail, account exists) ...