var normal = 0.6;
var hover = 0.8;

function prepare_menu() {
	$('b_1').setOpacity( normal );
	$('b_2').setOpacity( normal );
	$('b_3').setOpacity( normal );
	$('b_4').setOpacity( normal );
	$('a_1').observe ('mouseover', function() { $('b_1').setOpacity( hover ); });
	$('a_1').observe ('mouseout', function() { $('b_1').setOpacity( normal ); });
	$('a_2').observe ('mouseover', function() { $('b_2').setOpacity( hover ); });
	$('a_2').observe ('mouseout', function() { $('b_2').setOpacity( normal ); });
	$('a_3').observe ('mouseover', function() { $('b_3').setOpacity( hover ); });
	$('a_3').observe ('mouseout', function() { $('b_3').setOpacity( normal ); });
	$('a_4').observe ('mouseover', function() { $('b_4').setOpacity( hover ); });
	$('a_4').observe ('mouseout', function() { $('b_4').setOpacity( normal ); });
}

Event.observe(window, 'load', prepare_menu);