iPod Software 1.3.1 Updater installs the same software as iPod Software 1.3 Updater. The only difference is that iPod Software 1.3.1 Updater is compatible with Mac OS X 10.3, and iPod Software 1.3 Updater is not. If you don't have Mac OS X Panther, you don't need to use iPod Software Updater 1.3.1.
After using iPod Software 1.3.1 Updater, iPod's About screen will still read version 1.3, not 1.3.1. You can update to the latest version of the iPod software using Software Update or clicking the links below. 
iPod (with touchwheel and scroll wheel)
Download 
iPod 1.3 for Windows and 
iPod 1.3.1 for Mac OS X.
iPod (with Dock Connector)
iPod 2.1 for both Mac OS X and Windows is available from the 
iPod  Download page. 
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