function preload(imgObj,imgSrc) 
{
   eval(imgObj+' = new Image()')
   eval(imgObj+'.src = "'+imgSrc+'"')
}

preload('history_fr_on','/images/history_fr_on.gif');
preload('history_fr_off','/images/history_fr_off.gif');

preload('operations_fr_on','/images/operations_fr_on.gif');
preload('operations_fr_off','/images/operations_fr_off.gif');

preload('members_fr_on','/images/members_fr_on.gif');
preload('members_fr_off','/images/members_fr_off.gif');

preload('contact_info_fr_on','/images/contact_info_fr_on.gif');
preload('contact_info_fr_off','/images/contact_info_fr_off.gif');

function img_toggle( imgName, mode ) 
{
   if( document.images ) 
   {
      document[ imgName ].src = eval( imgName + "_" + mode + ".src" );
   }
}