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

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

function SwitchImage(id,name) {
    if (document.getElementById(id).checked == true) {
        document.getElementById(id).checked = false;
        document[name].src = unchecked.src;
    } else {
        document.getElementById(id).checked = true;
        document[name].src = checked.src;
    }
}