The process for loading the calculator with a new ROM image is fairly straightforward.
If you have the proper hardware, and a .BIN file, follow the instructions in the following file: Flashing a 20B calculator.
(Note: The instructions say that the PC must have a physical serial port however I was successfully able to flash the ROM from a copy of XP running under VMWare on a MacBook Pro using a GigaWare USB↔Serial converter bought from RadioShack. It was a good bit slower though so a physical port is advised if you are going to be uploading your own images frequently. BruceH)