I've been experiencing the same iPod mounting problems as many users since updating to 10.3.4. Until that point, everything worked flawlessly. After the upgrade, I've experienced the same issue as has been reported on various sites -- the iPod would not show up anywhere. Today, since I've had similar intermittent problems with my external FireWire drive, I tried plugging the iPod into the 'extra' FireWire 400 port on my ADS external hardrive (after the external drive showed up on the desktop). Guess what? The iPod was immediately recognized and performed a sync with iTunes.
The problem definitely is related to the OS / Security update and the FireWire ports on the computer. I'm running a G5 DP 2.0 Ghz with 8 Gigs of RAM. If you're having similar troubles and have access to another FireWire port, give it a try...
Mac OS X Hints
http://hints.macworld.com/article.php?story=200406252012423