Bad firmware zip file for Mac OS Fab ISP English instructions
The Firmware zip file under the Mac OS instructions is bad (linked like this "FabISP Firmware (right click save as)"); it cannot be opened successfully on Mac, listed as "invalid" by windows. This is the offending file:
Later in the Windows instructions, there is a good copy of the firmware linked ("5. Download the FabISP Firmware"). Here is the good file: http://academy.cba.mit.edu/classes/embedded_programming/firmware.zip
Probably the firmware_44.zip file should just be replaced with a firmware zip file that works (e.g. the CBA version), but alternately, the link could just be changed to the cba link.