simplepastiefile.js

var outer = $('theOuterBox');
var comp = $('theComparisonArea').update();
//you shouldn't need to change anything below this
var list = outer.childElements();
document.observe('click', function(evt){
  var elm;
  if(elm = evt.findElement('input[type="checkbox"]')){
    if((outer.select('input:checked').length + comp.select('input:checked').length) > 2){
      evt.stop();
      elm.checked = false;
    }else{
      comp.select('div').each(function(em){
        outer.insert(em.remove());
      });
      list.each(function(em){
        if(em.down('input:checked')){
          comp.insert(em.remove());
        }
      });
    }
  }
});