I decided to buy a firewire card this past weekend, so that I could finally play with an iPod I got for Christmas. The kudzu service picked it up and configured it easily enough, so I was ready to go.
A quick Google search revealed GNUpod, so I checked it out. Not only is the software very nice and useful, they have some excellent documentation that explains everything you could possibly want to know.
Since I had a Mac iPod and wanted to convert it to Windows, I simply followed their instructions in section 3.3. It explains using dd to make a backup of the firmware (which sits in its own partition) and then gives you the following command:
dd if=/dev/zero of=/dev/sda bs=1M count=10
So, my iPod is now completely wiped. The documentation then explains what the partition table should look like and gives you the dd command to load your firmware back. And, of course, it works like a charm. I was particularly fond of this series of steps, because I now know that I can try anything (like playing with the Linux on iPod project), and I can't possibly screw up my iPod bad enough to not be able to restore it (barring physical damage, of course).
Of course, you can just mount an iPod if your kernel supports the filesystem (HFS+ for the Mac one), and then get down to business with the GNUpod tools. There is also gtkpod if you prefer a GUI.
