[Old Pedant]

Well, first of all, you aren't really using basic JavaScript when you do that.

You are using the jQuery library. So some of the code is going to be a bit (or a LOT!) different than if you were using ordinary JavaScript.

It is kind of like you are using a GPS navigation system (e.g, a TomTom or similar) but never learned how to read a map. You are trusting that your navigation system will always know how to read the map for you.

But to directly answer your question:

<script type="text/javascript">
$(document).ready(function() {
    $('.slideshowA').cycle({
		fx: 'fade',
		speed: 4000,
		delay: 0
	});
    $('.slideshowB').cycle({
		fx: 'fade',
		speed: 4000,
		delay: -1000
	});
    $('.slideshowC').cycle({
		fx: 'fade',
		speed: 4000,
		delay: -2000
	});
});
</script>

I don't think you an make it much shorter than that without major changes to how you code it.