function switchMainImage(elementId, newSrc)
{
    obj = getObjectById(elementId);
    if(obj!=null)    
        obj.src = newSrc;
}

function getObjectById(elementId)
{
  if (window.document[elementId]) 
      return window.document[elementId];
  if (navigator.appName.indexOf("Microsoft Internet")== -1)
    if (document.embeds && document.embeds[elementId])
      return document.embeds[elementId];
    else
      return document.getElementById(elementId); 
  else
    return document.getElementById(elementId);
}