The following is a very nice solution to compare two strings in a case insensitive way, it uses the prototype functionality to add a method equalsIgnoreCase to the String class:

  <script type="text/javascript">

    String.prototype.equalsIgnoreCase=equalsIgnoreCase;
 
    function equalsIgnoreCase(arg) {               
      return (new String(this.toLowerCase())==(new String(arg)).toLowerCase());
    }

  </script>

You can use this new function in the following way:

  <script type="text/javascript">

    var text = "HELLO";
    alert(text.equalsIgnoreCase("hello"));

  </script>