var strImgDragging = null;        
var sidx = null;
var sidy = null;
var cnt = 0;

function mouseDownEvent()         
{
  strID = event.srcElement.id;
  
  if (strImgDragging == null) {
      if (strID.indexOf("P") != -1) {  
          strImgDragging = strID;       
          sidy = document.all[strID].style.pixelTop;
          sidx = document.all[strID].style.pixelLeft;
          document.all[strImgDragging].style.zIndex = 1;
          document.all[strImgDragging].style.border = "2px solid #000000";
      }
      else {
          sidx = null; sidy = null;
          strImgDragging = null;        
      }
  }
  else {
    if (strID.indexOf("P") != -1) {  
       document.all[strImgDragging].style.pixelLeft = 
          document.all[strID].style.pixelLeft;
       document.all[strImgDragging].style.pixelTop = 
          document.all[strID].style.pixelTop;
       document.all[strID].style.pixelLeft = sidx;
       document.all[strID].style.pixelTop = sidy;
       document.all[strImgDragging].style.border = "";
          document.all[strImgDragging].style.zIndex = -1;
    }
    sidx = null; sidy = null;
    strImgDragging = null;        

  }
  strID = null;
  event.cancelBubble = true;
  event.returnValue = false;

}

document.onmousedown=mouseDownEvent;