document.onkeypress = function (e) {

  e = e || window.event || {};
  var key = e.charCode || e.keyCode || e.which;

  if (key == 13)
  {
     var txt = document.getElementById('txtZip');

     if(txt.value.length > 0) 
     {
	var loc = "http://www.vegvine.com/?Z=" + txt.value;
	window.location = loc;
	return false;
     }
  }  

}