function imgSwap(oImg)
		{
		   var strOver  = "_on"    // image to be used with mouse over
		   var strOff = "_off"     // normal image
		   var strImg = oImg.src
		   if (strImg.indexOf(strOver) != -1) 
			  oImg.src = strImg.replace(strOver,strOff)
		   else
			  oImg.src = strImg.replace(strOff,strOver)
		}