If you try to install older iPod software onto a computer with Mac OS X 10.4 Tiger, you may see the following error message about a missing Mac OS X Networking Update:
iPod 2 Software cannot be installed on this computer. This update requires the Mac OS X Networking Update.
This can happen with any Mac with Mac OS X 10.4 or later when you try to use older iPod software. To avoid this, download and install the latest iPod Updater.