window.onload not working in IE

[Jon Hack]

Hello everyone, I know this should be simple but for some reason I
cant get the windows.onload to work in IE. It works fine in FF.

I've tried both of these blocks of code, and neither works.

window.onload = function() {
        alert('moo');
}

window.addEvent('load', function() {
        alert('moo');
});

I'd appreciate it if someone could point me in the right direction.
Thanks.

Note: in the end my function will do more than just an alert, but I'm
sticking to the basics for testing.