var _oldState;
function onMouseOver(el) {
    _oldState = el.src;
    el.src = el.src.replace("_out", "_over");
}

function OnMouseOut(el) {
    el.src = _oldState;
}

var hrefs = document.getElementById('divLeftMenu').getElementsByTagName("a");
var i = 0;
for (i = 0; i < hrefs.length; i++) {

    var imgs = hrefs[i].getElementsByTagName("img");

    var j = 0;
    for (j = 0; j < hrefs.length; j++) {
        if (imgs[j]) {

            imgs[j].onmouseover = function() { onMouseOver(this); };
            imgs[j].onmouseout = function() { OnMouseOut(this); };
        }
    }
}