Jaguar seems to have a problem loading on these. I use Panther and have even used tiger by removing the hard drive and installing it using another machine. They use Safari Camino and Firefox just fine. Make sure you have at least 256MB of ram. You might have to boot from your 9.1 disk first and run the firmware update which is on that disk. I have rebuild 5 or 6 of these and they still work well.