function toggleLayer(whichLayer)
{
    if (document.getElementById)
    {
        // this is the way the standards work
        var style2 = document.getElementById(whichLayer).style;
        style2.display = style2.display? "":"block";
    }
    else if (document.all)
    {
        // this is the way old msie versions work
        var style2 = document.all[whichLayer].style;
        style2.display = style2.display? "":"block";
    }
    else if (document.layers)
    {
        // this is the way nn4 works
        var style2 = document.layers[whichLayer].style;
        style2.display = style2.display? "":"block";
    }
}

var count = 0;

function swap() {

switch (count % 3) {
case 0:
toggleLayer("block1");
toggleLayer("block2");
break;
case 1:
toggleLayer("block2");
toggleLayer("block3");
break;
case 2:
toggleLayer("block3");
toggleLayer("block1");
break;
}

count++;

}

var messageCounter = 0; // initialize message counter
var timeDelay = 10000; // milliseconds between updates

function Update() {
   swap();
   timerID = setTimeout("Update()", timeDelay);
}

function Start() {
   timerID  = setTimeout("Update()", timeDelay);
}

function Stop() {
   if(timerID) {
      clearTimeout(timerID);
      timerID  = 0;
   }

   tStart = null;
}