I've found numerous references to setting the first option in the msdropdown using this code:
var oHandler = $('#input_zip').msDropDown().data("dd");
Now, in IE8, I'm seeing a problem with this as I get the "A script on this page is causing Internet Explorer to run slowly..." error dialog when executing the first line.
I know it's the code above causing it because I've added breakpoints to see. If I use this code:
$('#input_zip').msDropDown().setValueByIndex ("selectedIndex", 0);
It does essentially the same thing and I still get the error.