function new_window(page,w,h) {
  var leftdist = (window.screen.availWidth - w)/2;    // distance to left edge of window
  var topdist = (window.screen.availHeight - h)/2;     // distance to top edge of window

  page=escape(page);
  page=page.replace(/%3A/,":");
  page=page.replace(/%3F/,"?");
  page=page.replace(/%26/g,"&");
  page=page.replace(/%3D/g,"=");

  my_win=window.open(page,'new_window','left='+leftdist+',top='+topdist+'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizeable=1,width='+w+',height='+h);
  my_win.focus();
}

function user_file(id) {
  new_window('/user_file.php?id='+id,500,500);
}