if (document.images) {
    // preload the alternate images offscreen
   homeon = new Image();
   homeon.src = "images/42-on.gif";
   practiceon = new Image();
   practiceon.src = "images/43-on.gif";
   patienton = new Image();
   patienton.src = "images/44-on.gif";
   dentiston = new Image();
   dentiston.src = "images/45-on.gif";
   caseon = new Image();
   caseon.src = "images/46-on.gif";
   seminaron = new Image();
   seminaron.src = "images/47-on.gif";
   contacton = new Image();
   contacton.src = "images/48-on.gif";
   homeoff = new Image();
   homeoff.src = "images/42-off.gif";
   practiceoff = new Image();
   practiceoff.src = "images/43-off.gif";
   patientoff = new Image();
   patientoff.src = "images/44-off.gif";
   dentistoff = new Image();
   dentistoff.src = "images/45-off.gif";
   caseoff = new Image();
   caseoff.src = "images/46-off.gif";
   seminaroff = new Image();
   seminaroff.src = "images/47-off.gif";
   contactoff = new Image();
   contactoff.src = "images/48-off.gif";
}

function imgAct(imgName) {
  if (document.images) {
     document[imgName].src = eval(imgName + "on.src");
 }
}

function imgInact(imgName) {
  if (document.images) {
     document[imgName].src = eval(imgName + "off.src");
 }
}