A CID-unlocked device (it will NOT work if it's NOT CID-unlocked!)
A SD card of 128MB or larger (buy a 128MB for just this purpose, as its a great backup device)
To Dump the ROM:
Get into the tri-color screen (bootloader) (hold CAMERA, reset) and plug into the USB port.
Kill wcescomm.exe from Windows XP using the Task Manager (CTRL-ALT-DELETE) (this is the ActiveSync driver for the USB port)
Start Tera Term
Selec the "serial" radio button and from the drop down list select "USB"
Hit "return" to ensure you have a command prompt.
Make sure your 128MB SD card is in the slot.
Type "r2sd all" and hit return.
The loader will dump the entire ROM (including extended ROM) to the SD card.
Note that this is NOT a file on a FAT filesystem - its a RAW data dump with a signature and checksum. As such you CAN NOT read it onto your computer - you need a tool like "psdread" to read it from the card to a file on your PC.
Stick the card somewhere safe.
To Restore the ROM:
Insert the SD with the power off in the Prophet, then power on while holding the CAMERA button.
Press the Comms button on the side when it tells you.
Note that the prompt only comes up for a few seconds and then it will continue to enter the bootloader.
ftp://xda:xda@ftp.xda-developers.com//Uploads/Prophet/Prophet-tools/TeraTermPro_WinCE_USB.zip