For those interested I hacked on the Xpad driver for the kernel and got the RockBand Harmonix guitar to work with FretsonFire.  Works pretty nice.

Just put these 3 files (Makefile, xpad.c, xpad.h) in a directory, cd into the directory
make
sudo make install


then add these lines to your /etc/modules
usbcore
joydev
xpad

reboot (gey)
dont plug the guitar in until after you login.

Then you can run jscalibrator to verify the guitar is working.
run fretsonfire and change the keys to match the guitar frets
woo thats it.
play at will

UPDATE: fixed typo 

Added a forum for discussion of the drivers.