If you have "Room" installed, there is a menu option to format the player. Â I think doing this in "Room" will also reload the GBSYSTEM directory with the factory bootloader. Â If not, if you look in the Toshiba folder where Room is installed, you should see a GBSYSTEM folder. Â (It may be hidden so make the proper adjustments to your OS to view hidden files/folders.) Â Just copy the GBSYSTEM folder back to the root of your Gigabeat. Â Slide the battery switch off then on again and you're back in the original firmware.
Calling Toshiba will get you the Manufacturer's Official CD with the updated version. Â From what I hear, it's free and has the updated version. Â All of that stuff mentioned above is on that CD.
BTW, just to make sure you are clear, the Original Firmware is basically just the unedited GBSYSTEM directory.