You have to first select “Enable FireWire disk use” in iPod Preferences in iTunes. This option is off by default. To change iPod Preferences in iTunes, connect your iPod to your Mac, then start iTunes. Select your iPod in the source list on the left and click the iPod icon in the lower right corner of the screen.
My iPod does not show up as an icon in Finder or on my Mac’s desktop. How can I use it as an external FireWire drive then?