Method to downgrade iPod software from 1.1 to 1.0.3
http://discussions.apple.com/thread.jspa?threadID=1347183&tstart=0
To get back to 1.0.3, first go to your User Library > iTunes > iPod and remove the two files labeled as "iPod_26.1.1". I also removed any "previous iTunes Libraries" from my User Documents > Music folder. Then turn off your internet connection to prevent an automatic update to version 1.1. After opening iTunes and connecting the iPod, you can then "Restore", and it will ask if you want the previous version that you have in your library. After restore and sync, you're back in business!!
G5-Dual 2.5, Mac OS X (10.4.11), 4 gig RAM