var logo_on = new Image();
logo_on.src = 'images/mini_on.gif';

var logo_off = new Image();
logo_off.src = 'images/spg.gif';

function roll_on(x) {
	var y = eval('document.roll_' + x.name);
	y.src = logo_on.src;
}

function roll_off(x) {
	var y = eval('document.roll_' + x.name);
	y.src = logo_off.src;
}