allDivs = {
	0: 'block-01', 
	1: 'block-02', 
	2: 'block-03', 
	3: 'block-04'
};

function showDiv(div) {
	$(div).style.visibility = 'visible';
}

function hideDiv(div) {
	$(div).style.visibility= 'hidden';
}

function init() {
	if (!$('block-01')) return;
	for (var key in allDivs) {
		$(allDivs[key]).onmouseover = function() {
			var currentDiv = this.id;
			showDiv(currentDiv + '-sub');
			return false;
		}
		$(allDivs[key] + '-sub').onmouseover = function() {
			var currentDiv = this.id;
			showDiv(currentDiv);
			return false;
		}
		$(allDivs[key]).onmouseout = function() {
			var currentDiv = this.id;
			hideDiv(currentDiv + '-sub');
			return false;
		}
		$(allDivs[key] + '-sub').onmouseout = function() {
			var currentDiv = this.id;
			hideDiv(currentDiv);
			return false;
		}
	}	
}

Event.observe(window, 'load', init, false);