var num;
num=0;
setTimeout('change_img()',5000);

function change_img(){
if(num>3) num=0;
setTimeout('setFocus('+num+')',5000);
num++;
tt=setTimeout('change_img()',5000);
} 

function setFocus(id)
{
selectLayer(id);
}

function selectLayer(id)
{
var layers=[document.getElementById("idNum0"),document.getElementById("idNum1"),document.getElementById("idNum2"),document.getElementById("idNum3"),document.getElementById("idNum4"),document.getElementById("idNum5")];

           for(var i=0;i<layers.length;i++)
{
if(i==id)
{
layers[i].style.display="block";
}
else
{
layers[i].style.display="none";
}
}
}