function tab(obj,num,name){
    var max = document.getElementsByName(name);
    for(var i=1; i<=max.length; i++){
        var txt=max[i-1].src;
        var lastIndex=txt.lastIndexOf("_");
        if(i == num){
            if(txt.substring(lastIndex+1) != '.gif'){
                document.getElementById(obj+i).style.display = 'block';
                max[i-1].src = max[i-1].src.replace(".gif","_.gif");
                max[i-1].parentNode.className='on';
            }
        }else{
            document.getElementById(obj+i).style.display = 'none';
            max[i-1].src = max[i-1].src.replace("_.gif",".gif");
            max[i-1].parentNode.className='';
        }
    }
}