$(document).ready(
function() {
	$('#slideshow').cycle({
		timeout: 0,
		next: "#next_image",
		prev: "#prev_image",
		before: checkCycle,
		slideExpr: "img",
		height: "500px"
	});
//after:         null,  // transition callback (scope set to element that was shown)
//height:       'auto', // container height
});

function checkCycle() {
	if ($(this).hasClass('first')) {
		$("#prev_image").addClass("last");
	} else {
		$("#prev_image").removeClass("last");
	}

	if ($(this).hasClass('last')) {
		$("#next_image").addClass("last");
	} else {
		$("#next_image").removeClass("last");
	}
}