var checked = new Image();
var unchecked = new Image();

checked.src = '/images/checked.gif';
unchecked.src = '/images/unchecked.gif';

function SwitchImage(menunum) {
	for (i = 1; i<=4; i++){
        document.getElementById('my_check' + i).checked = false;
        document['check_image' + i].src = unchecked.src;
	}
    if (document.getElementById('my_check' + menunum).checked == true) {
        document.getElementById('my_check' + menunum).checked = false;
        document['check_image' + menunum].src = unchecked.src;
    } else {
        document.getElementById('my_check' + menunum).checked = true;
        document['check_image' + menunum].src = checked.src;
    }
}