document.observe('dom:loaded', function() {
	$$('#navigation a').invoke('observe', 'mouseover', observeOver);
	$$('#navigation a').invoke('observe', 'mouseout', observeOut);
});


function observeOver(event) {
	var elementClassName = this.readAttribute('class');
	$('nav_' + elementClassName ).addClassName('nav_' +  elementClassName + '_hover');
}

function observeOut(event) {
	elementClassName = this.readAttribute('class');
	$('nav_' + elementClassName).removeClassName('nav_' + elementClassName  + '_hover');
}