"jQuery" is undefined (IE Only)

"jQuery" is undefined (IE Only)

OK... this is probably a dumb question but something I keep running into in IE.

I've got a few plugins that I am using and for whatever reason, IE is having problems running them.  The format for both of the plugins is this:

(function($){
      $.fn.pluginName = function(opts) {
      -- stuff --
      }
})(jQuery);

It seems like IE is not able to define the (jQuery) piece at the end of the function.  If I change these plugins to the regular format and not worry about other library conflicts... it works.  Does this make sense?  Do I have to define what jQuery is somewhere else?  I'm pulling in the latest jQuery file through the following:

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js"></script>

Any help you can provide to help me understand why I am getting conflicts in IE and not other browsers will be much appreciated.

Thanks.