function chgImg(imgField,newImg)
{
  if(document.images)
  {
    document[imgField].src= eval(newImg + ".src")
  }
}

function preLoadImages()
{
  if(document.images)
  {
    if(!document.preloadedImages) document.preloadedImages=new Array();
    var c,args=preLoadImages.arguments;
    for(c=0; c<args.length; c++)
    {
      document.preloadedImages[c]=new Image;
      document.preloadedImages[c].src=args[c];
    }
  }
}

function go(page)
{
  window.document.location = page;
}

function popup(page, name, width, height, scrollbars)
{
  var x = (screen.width - width) / 2;
  var y = (screen.height - height) / 2;
  newWindow = window.open(page,name,'width='+width+',height='+height+',left='+x+',top='+y+',scrollbars='+scrollbars+',resizable,menubar=no')
  if (parseInt(navigator.appVersion) >= 4)
  {
    newWindow.window.focus();
  }
}

function required(field,message)
{
  if (field.value.length == 0)
  {
    alert(message);
    return false;
  }
  return true;
}

function loadImg(imageName)
{
  i = new Image();
  i.src = imageName;
  return i;
}

function postCodeLength(field, message) {
	var error="";
	if (field == null) {
		error = "Internal Error - Unable to locate the required field";
		return error;
	}

	var strng = field.value;
	if (strng == "") {
		error = "You need to enter a valid 4 digit post code.\n";
	}
	var illegalChars = /[\W_]/; // allow only letters and numbers
 	if ((strng.length < 4) || (strng.length> 4)) {
		error = message+" You need to enter a valid 4 digit post code\n";
	} else if (illegalChars.test(strng)) {
		error = message+" contains illegal characters.\n";
	}
	return error;
}