Version of jQuery: 1.3.2

I'm a js noob, way over my head. Please be kind!

The global .js for our site contains this statement:

document.getElementsByClassName = function(className, parentElement) {
  var children = ($(parentElement) || document.body).getElementsByTagName('*');
  return $A(children).inject([], function(elements, child) {
    if (child.className.match(new RegExp("(^|\\s)" + className + "(\\s|$)")))
      elements.push(child);
    return elements;
  });
}

The Tabs widget works fine in FF, Chrome, Opera, but in IE8 I get this error:

Object doesn't support this property or method.

When I look at Firebug, the error console says:

Error: ($(parentElement) || document.body).getElementsByTagName is not a function 

After googling, I tried replacing .getElementsByTagName('*') with 

.getElementsByTagName('param') and .getElementsByTagName('object'), 

but neither worked.

Any help would be appreciated!