Ruby on Rails : Dynamic drop down list - onchange

In views page

  <% @people = Person.find(:all) %>  
  <%= javascript_include_tag "prototype" %>

  <%= collection_select :person, :id, @people, :id, :firstname, 
  {:include_blank => false}, 
  {:onchange => remote_function(:url => {:action => 'say_hello'},
  :with => "'id=' + this.value",
  :update => "mydiv")} %>
  
  <div id="mydiv">
  <%= render :partial => "people/show"%>
  </div>

In controller

  def say_hello
     @person = Person.find(params[:id])  
     render :partial => "people/show"
  end

Taken From : http://www.ruby-forum.com/topic/187488 [RoR & Ajax]
Other Resource : http://delta-knight.co.uk/jump-to.shtml [HTML & JS]