http basic authentication and restful authentication

hey,

I have created a web app in Ruby On Rails and users can login and
register with resftul authentication.
Now I am creating an Android application where the user can access
some parts of the website (xml resources).
To access these xml files with HTTP GET Request the username and
password from the user has to be sended with this request to
authenticate the user. Now this can be done with http basic
authentication but when i put this code in my authentication file:

    def login_from_basic_auth
      authenticate_or_request_with_http_basic do |username, password|
        self.user = User.authenticate(username, password)
      end
    end

i only can login at my site when i fill in username and password in a
dialogue. How can I disable this so the user at the website can login
normally trough login form (and register) and only enable the login
with basic authentication for request from my android application?

How can a user register on my site when he has to fill in first a
username and password..

Please help me,

Thank you

Wouter

Please help me!

Thanx