I was able to do the roll back/downgrade from 1.1 to 1.0 by doing the edit of the Sysinfo file. I have a 5th gen 60gig and it worked flawlessly. I would suggest making sure you have all of your files backed up and copy the Sysinfo file to your desktop before you go and try editing it. Good Luck! Here are the instructions from the previous page:
Put the ipod in harddisk mode
edit the file (hidden folder and file)
\iPod_Control\Device\SysInfo
Replace the line that have the word "buildID" with this line:
buildID: 0x05108000 (6.1)
run iPod Updater 2005-11-17.exe or iPod Updater 2005-10-12.exe (both have the same software version for ipod video 5th generation)
iPod Updater 2005-11-17.exe can be downloaded from:
http URL
appldnld.m7z.net/content.info.apple.com/iPod/ww/win/061-2225.20051128.PDWnw/iPodSetup.exe
Select upgrade (with this options you dont delete the songs or videos inside the ipod, if you select restore you lose all the content inside the ipod)
After that, you have your IPOD with version 1.0 and you can watch your videos without a problem again
