on = new Image();
out = new Image();
on.src="/images/arrow_v.gif";
out.src="/images/arrow_g.gif";

function point(id){
var el=document.getElementById(id);
el.style.backgroundImage='url('+on.src+')';
}

function unpoint(id){
var el=document.getElementById(id);
el.style.backgroundImage='url('+out.src+')';
}