function imgSwap(oImg)

{

   var strOver  = "_over"    // 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)

}