I don't think we're technically allowed to share Apple's firmware (hides under desk to escape people throwing stuff). That being said, how do you plan to flash the firmware while your computer cannot see the iPod at all? Does the iPod boot? Can you manipulate it into disk mode (hold center button and "menu" button for a few seconds until you see Apple's logo, then quickly switch to holding the center button and the "play/pause" button)? As far as I know, a different firmware won't help you if your iPod won't show up in Windows Explorer or My Computer. (you are running Windows, aren't you?)
If you can get it into disk mode, try Apple's firmware utility again. Do a full restore. If you get it to the point where the Rockbox install tools work, Apple's updater utility should work.
Good luck,
JBot
PS. if you explain why you need my firmware--the Apple updater won't work at all, but the Rockbox patch utilities do--I am willing to share. I am not just going to default to that, though.