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

preload('fiscal_policy_fr_on','/images/fiscal_policy_fr_on.gif');
preload('fiscal_policy_fr_off','/images/fiscal_policy_fr_off.gif');

preload('tax_policy_fr_on','/images/tax_policy_fr_on.gif');
preload('tax_policy_fr_off','/images/tax_policy_fr_off.gif');

preload('monetary_policy_fr_on','/images/monetary_policy_fr_on.gif');
preload('monetary_policy_fr_off','/images/monetary_policy_fr_off.gif');

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