It is also possible to mount the iPod via Firewire. I have this currently setup in Fedora Core 1 using a firewire PCI card. Firewire support in Kernel 2.4.22 is shoddy at times. Hotplug doesn't always work. I believe 2.6.x kernel supports hotplug much better, and I will try later on with that.
Using Firewire versus USB is nearly identical. The difference is getting the kernel to recognize the iPod as a SCSI device on sda and then pointing the device to /mnt/ipod. Once that is done, the rest of the process is identical to the USB instructions that Aric posted.
Word of warning:
Don't use other Non-iTunes iPod software with the iPod - if you have purchased songs from the Apple iTunes music store. Songs that are purchased (.m4p or .m3a files) will not be read correctly and could corrupt the itunesDB file. I learned this the hard way using Ephpod and GTKPod on Linux.
So in closing, making iTunes work on Linux is a must!