using Event.observe for when a page loads (See related posts)

Event.observe( window, 'load', function() {
  // Put the Javascript that needs to happen when the page
  // loads here
} );

Event.observe( window, 'load', function() {
  var inputs = document.getElementsByTagName( 'input' );
  var textareas = document.getElementsByTagName( 'textarea' );

  for ( var i=0; i<inputs.length; i++ ) {
    type = inputs[i].type;

    if (
      ( type == 'button' || type == 'reset' ||
      type == 'password' || type == 'text' ||
      type == 'submit' ) &&
      ( inputs[i].onfocus == '' ||
      !inputs[i].onfocus )
    ) {
      inputs[i].onfocus = function() {
        this.className = 'selected';
      }

      inputs[i].onblur = function() {
        this.className = '';
      }
    }
  }

  for ( var i=0; i<textareas.length; i++ ) {
    if ( textareas[i].onfocus == '' || !textareas[i].onfocus ) {
      textareas[i].onclick = function() {
        this.className = 'selected';
      }
      textareas[i].onblur = function() {
        this.className = '';
      }
    }
  }
} );