var ie4 = (document.all) ? true : false;

var ns6 = (document.getElementById && !document.all) ? true : false;

function swapImage(imageNumber)
{
  if (ie4)
  {
	  document.all.mainImage.src = "../images/portfolio/studio/"+imageNumber+".jpg";
  }
  else if (ns6)
  {
	 document.getElementById('mainImage').src = "../images/portfolio/studio/"+imageNumber+".jpg";
  }
}