i had the same problem with my iphone,
not sure if this will work on the ipod, but its worth a try,
back up and delete:
hd/system/libary/privateframeworks/mobiledevice.framework, and the uninstall itunes (i used appdelete for my mac
http://www.versiontracker.com/dyn/moreinfo/macosx/31123)
empty trash. re install itunes (7.5 worked great for me) reboot,
then, reset ipod (hold down sleep and home together, wait until silver apple appears then let go of sleep still holding home, untill contect to itunes appears. )
option restore, navagate to the firmware you want, and it should work.
if not im sorry i cant be of anymore help,
good luck