Prototype JS Document.observe Doesn't Work In IE 6??

I'm using the Prototype JS framework. why this doesn't work in IE6?

Code:
document.observe('dom:loaded', function(e){alert("hello world");});

It should just fire off an alert once the page loads, but does nothing, no errors either. Of course it works fine in Firefox.

Test it out here (the alert message is slightly different but everything else is the same, you'll want to remove the spaces in the url of course): www-stage . emd . wa . gov / dev / kids / dev / prototype_test . htm