Password
Confirm
 

Rails code explained

You just need to add on line in your view and two more options to the form_remote_tag.

To generate code for overlay message:

<%= transparent_message_create("ajax_info_message", "Saving password<br/>", "/images/progress_FFF.gif") %>

To display/hide overlay message add :loading and :complete options

<%= form_remote_tag( :url => {:action => "post"}, 
                     :html => {:id => "password_form"},
                     :loading  => transparent_message_show('ajax_info_message', {:hideMode => "'none'", 
                                                                                 :showMode => 'null', 
                                                                                 :insideElement => {:id => "'form'"}}), 
                     :complete => transparent_message_hide('ajax_info_message')) %>

CSS File (toggle)

/* Transparent form message (error and notice) for ajax form */
.transparent_ajax_message {
  width: 100%;
  text-align: center;
  font-size: 20px;
  position: absolute;
  opacity:  0.8;
}

.transparent_ajax_error p {
  color: #560109;
  background: #FFA3A9;
  
  border-left: 1px solid #750004;
  border-right: 1px solid #750004;
  border-bottom: 1px solid #750004;  
  margin: 0px 20px 0px 20px;
  padding-top: 20px;
  padding-bottom: 20px;
  -moz-border-radius-bottomleft: 10px;
  -moz-border-radius-bottomright: 10px;
}

.transparent_ajax_notice p {
  color: #23571D;
  background: #9BFFA3;
  
  border-left: 1px solid #23571D;
  border-right: 1px solid #23571D;
  border-bottom: 1px solid #23571D;  
  margin: 0px 20px 0px 20px;
  padding-top: 20px;
  padding-bottom: 20px;
  -moz-border-radius-bottomleft: 10px;
  -moz-border-radius-bottomright: 10px;
}


/* Saving message for ajax form */
#ajax_info_message {
  position: absolute;
  background: #FFF;
  opacity:  0.7;
}

#ajax_info_message p {
  padding-top: 0px;
  font-size: 30px;
  color: #B1A861;
  text-align:  center;
}

Full view code (toggle)

<%= transparent_message_create("ajax_info_message", "Saving password<br/>", "/images/progress_FFF.gif") %>
<div class="form" id="form">    
  <div class="form_content">    
    <%= form_remote_tag(:url => {:action => "post"}, 
                        :html => {:id => "password_form"},
                        :loading  => transparent_message_show('ajax_info_message', {:hideMode => "'none'", :showMode => 'null', :insideElement => {:id => "'form'"}}), 
                        :complete => transparent_message_hide('ajax_info_message')) %>
      <span class="label">Password</span><span class="field"><%= password_field_tag "password" %></span><br class="clear"/>
      <span class="label">Confirm</span><span class="field"><%= password_field_tag "confirm" %></span><br class="clear"/>
      <span class="label"> </span><span class="field"><%= submit_tag "Save" %></span><br class="clear"/>
    <%= end_form_tag %>
  </div>
</div>