function openWindow(url, name, w, h) {

  // initialize winX and winY to default values

  // for cases where Screen object isn't supported

  var winX = 0;

  var winY = 0;

  h = h + 20;

  w = w + 20;

  

  // only set new values if 4.0 browser

  if (parseInt(navigator.appVersion) >= 4) {

    winX = (screen.availWidth - w)*.5;

    winY = (screen.availHeight - h)*.5;

  }



  popupWin = window.open(url, name, 'width=' + w + ',height=' + h + ',left=' + winX + ',top=' + winY);

}







 

//this is what your link shold look like:

//<a href="javascript:openWindow('../images/photobig.jpg', 1, 500, 371);"><img src="../images/photo.jpg"...