Javascript popup

1

Im trying to get o popup window to show a fullsize image from a thumbnail thats been clicked. I can get it to do this but only if you close the popup window between images.

My code atm is:

 function getHref()
 {
  //customize the window that gets opened 
  // 0 equals NO. 
  // 1 equals YES.
  desc = description[p];
  address = href[p]; 
  target_winName = fullSizePictures; 
  width = picWidth[p]+20;
  height = picHeight[p]+30; 
  toolbar = 0; 
  location = 0; 
  directories = 0; 
  status = 0; 
  menubar = 0; 
  scrollbars = 0; 
  resizable = 0; 
  //sends data back to the function 
  openWinCentre(desc, address, target_winName, width, height, toolbar, location, directories, status, menubar, scrollbars, resizable);
 }
 
_root.openWinCentre = function (desc, url, winName, w, h, toolbar, location, directories, status, menubar, scrollbars, resizable) { 
getURL ("javascript:var myWin; if(!myWin || myWin.closed){myWin = window.open('" + url +"','" + winName + "','" + "width=" + w + ",height=" + h + ",toolbar=" + toolbar + ",location=" + location + ",directories=" + directories + ",status=" + status + ",menubar=" + menubar + ",scrollbars=" + scrollbars + ",resizable=" + resizable + ",top='+((screen.height/2)-(" + h/2 + "))+',left='+((screen.width/2)-(" + w/2 + "))+'" + "');}else{myWin.focus();};void(0);"); 
}

Ive tryed all manner of things to no avail, ive also searched for tutorials and web help but found nothing that works!!