matchHeight=function(){
        var divs,contDivs,maxHeight,divHeight,d;
        var div_extra,div_extrab,div_posts;

        /* <div> a redimensionar */
        div_extras=document.getElementById('sec');
        div_extrasb=document.getElementById('sec');
        div_posts=document.getElementById('col-tres');
        divs=[div_extras,div_extrasb,div_posts];
        contDivs=[];

        /* altura maxima */
        maxHeight=0;

        /* procura altura maxima dos <div> */
        for(var i=0;i<divs.length;i++){
            d=divs[i];
            if (d) {
                contDivs[contDivs.length]=d;
                if(d.offsetHeight){
                    divHeight=d.offsetHeight;
                }
                else if(d.style.pixelHeight){
                    divHeight=d.style.pixelHeight;
                }
                maxHeight=Math.max(maxHeight,divHeight);
            }
        }

        /* redimensiona os <div> */
        for(var i=0;i<contDivs.length;i++){
            contDivs[i].style.height=maxHeight+"px";
        }
    }

/* Executa o script */ 
window.onload=function(){
    if(document.getElementById){
        matchHeight();
    }
}