customer signup/login with Multi-forms

I would like to know the best rout to build this and what, if any open source or tutorials sites you could point me to.

A log-in/sign-up box that I can place on an html page. Once customer logs in, I would like a greeting message on their account page, with links that will open a form in a window, div, or iFrame. Once the person has filled out the form the data is email to email address(s) of my choosing, but also have the data in the already filled out form to stay populated with the option for the client to make changes and save the information.

The main action would be once a person either clicks “submit” or “save” the information would be emailed to someone.

Any help in pointing me in the right direction would be awesome!

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