you cant do this using a hidden form element since you need to lookup the value when the form submits.
use a text box to enter the email address.
Create a recordset that filters the email column on the email form element.
Use the Set Session Value server behavior to capture the email address in a session variable.
Again, use the set session value to capture the password.
In universal Email, Click the Dreamweaver icon to use Dreamweaver to create your email message.
Where you wish to display the password, use the session bindings group.