allora fai così:

<script>
function mouseover(cosa){
var l = parent.NOMEDELFRAME.location.href;
l = l.substring(l.lastIndexOf("/")+1,l.lastIndexOf("."));
if(l!=cosa)
document.images[cosa].src = "img/titoli/"+cosa+"over.gif";
}

function mouseout(cosa){
var l = parent.NOMEDELFRAME.location.href;
l = l.substring(l.lastIndexOf("/")+1,l.lastIndexOf("."));
if(l!=cosa)
document.images[cosa].src = "img/titoli/"+cosa+".gif";
}

function mousedown(cosa){
var l = parent.NOMEDELFRAME.location.href;
l = l.substring(l.lastIndexOf("/")+1,l.lastIndexOf("."));
if(l!=cosa)
document.images[cosa].src = "img/titoli/"+cosa+"down.gif";
}

function mouseup(cosa){
var l = parent.NOMEDELFRAME.location.href;
l = l.substring(l.lastIndexOf("/")+1,l.lastIndexOf("."));
if(l!=cosa)
parent.NOMEDELFRAME.onload = function() {
document.images[cosa].src = "img/titoli/"+cosa+".gif";
};
}
</script>

<a onmouseover="mouseover('chi')"; onmouseout="mouseout('chi')" onmousedown="mousedown('chi')" onmouseup="mouseup('chi')">[img]img/titoli/chi.gif[/img]</a>

in alternativa alla parte in grassetto potresti provare
setTimeout('document.images[cosa].src = "img/titoli/"+cosa+".gif";',5000);