var d = document;

function threeColumn(){

    var box = new Array("sidebar-a","content","sidebar-b"); //list of DIV ids
    for(x=0;x<box.length;x++){ //determine the tallest div
      h = d.getElementById(box[x]).offsetHeight;
      for(y=0;y<box.length;y++){
        
		
		test_h = d.getElementById(box[y]).offsetHeight;
        if(h<test_h) h = test_h;
      }  
    }
    for(x=0;x<box.length;x++) d.getElementById(box[x]).style.height = h +"px"; //set the height of all divs to the tallest
}