you will need some hand coding for this.
create a recordset to look up the entered username, another to lookup the entered password.
add a set session value behavior to store the username if the username record is not empty.
add another for the password if the password recordset is not empty.
use those session to populate the text fields.
if you need help configuring this, I suggest a premiere support appointment:
http://www.webassist.com/premier_request.php