var divds=["resizeDivs"] //Enter id(s) of each div

function resizeDivs(){

   for (var i=0; i<divds.length; i++){    
	var div1 = document.getElementById('column1').offsetHeight;
      	var div2 = 0;
      	var div3 = 0;

      	if( document.getElementById('column2of3') ){
		var div2 = document.getElementById('column2of3').offsetHeight;
		var div3 = document.getElementById('column3').offsetHeight;
      	}		
      	else{
		var div2 = document.getElementById('column2').offsetHeight;
      	}
      
      	var max = 0;
      
     	 if( div1 > div2 ){
		max = div1;
      	}
      	else{
		max = div2;
      	}
      
      	if( div3 > max ){
		max = div3;
      	}
      
      	max += "px";
      
     	document.getElementById('column1').style.height = max;
  
      	if( document.getElementById('column2of3') ){

		document.getElementById('column2of3').style.height = max;
      	}
      	else{
		document.getElementById('column2').style.height = max;
      	}
   }
}

if (window.addEventListener)
window.addEventListener("load", resizeDivs, false)
else if (window.attachEvent)
window.attachEvent("onload", resizeDivs)