##Controller - users_controller.rb

  def register
    if request.get?
      @user = User.new
    else
      @user = User.new(params[:users])
      if @user.save
        flash[:notice] = "User #{@user.email} created"
        redirect_to(:action => 'index')
      end
    end
  end

##Model - user.rb

require 'digest/sha1'

class User < ActiveRecord::Base
    attr_accessor :password
    attr_accessible :email, :password
    validates_uniqueness_of :email, :message => "already exists in the database"
    validates_presence_of :email, :password
    validates_format_of :email, :with => /^([^@\s] )@((?:[-a-z0-9] \.) [a-z]{2,})$/i,
              :message => "Invalid email address."


    def self.login(email, password)
      password_hash = encrypt(password || "")
      find(:first, :conditions => ["email = ? and password_hash = ?", email, password_hash])
    end

    def try_to_login
      User.login(self.email, self.password) ||
      User.find_by_email_and_password_hash(email, "")
    end

    def before_create
      self.password_hash = User.encrypt(self.password)
    end

    def after_create
      @password = nil
    end

    private
    def self.encrypt(password)
      Digest::SHA1.hexdigest(password)
    end
  end

## view - register.rhtml

<%= form_tag %>
<%= error_messages_for 'user' %>
<table>
  	<tr>
    	<td><label>Email:</label></td>
    	<td><%= text_field "users", "email" %></td>
  	</tr>
	<tr>
		<td><label>Password:</label></td>
		<td><%= password_field "users", "password" %></td>
	</tr>
	<tr>
		<td><label>Password Confirmation:</label></td>
		<td><%= password_field "users", "password_confirmation" %></td>
	</tr>
	<tr>
		<td><label>Select an Installation</label></td>
		<td><%= collection_select("users", "installation_id", @installation, :id, :basename, {:prompt => "--"})%></td>
	</tr>
	<tr>
		<td></td>
		<td style="text-align: right;"><%= submit_tag "Register" %></td>
	</tr>
</table>
<%= end_form_tag %>