I thought I would resurrect this thread to add some information I've just gotten about using iPods as external storage for a Zaurus. It is possible, although there are a few things to keep in mind. First, the iPod needs to be formatted on Windows to be readable by the Zaurus. Also, you have to go into the iPod preferences within iTunes and check the "enable disk use" box. Once you do this, you can connect it to the Zaurus with the USB host cable. I don't know precisely which models are compatible. The ones that predate the dock connector were firewire only, so they won't work for sure. I've tried it out with a 40GB 3rd generation model, and I've read of people using Shuffles and nanos. I'm sure the current full-sized iPods will work as well.
Auto-mounting of the iPod does not appear to work (from what I've read anyway). You need to manually mount it from the terminal. The Japanese website I found used this command:
mount -t vfat -o iocharset=utf8,codepage=932 /dev/sda2 /mnt/usbstorage
But I'm not sure that all of it is necessary. The data storage part of the iPod shows up under /dev/sda2.
Depending on the model of iPod you have, it may charge from the Zaurus when plugged in. That may be good or bad depending on your point of view. If you'll mostly be using it when plugged in, having an iPod that charges would be good, because you could use it for as long as you want without running out of power. But if you will be using it on batteries, having one that doesn't charge might be best, because it wouldn't sap power from your Zaurus battery. My 3rd gen iPod can use USB, but apparently can't charge from it, so it runs off its own internal battery.
I tried playing a divx file directly off of the iPod and it played fine. However, since my iPod doesn't get power while connect to the Zaurus, I have to be careful about running down the battery. I don't know how long it would last, but probably not all that long with constant disk access. I also copied the same divx file from the iPod to the internal microdrive of the Zaurus. I didn't pay too close attention to the time, but I think it took around 15 minutes to copy a file of around 400 mb.
I think getting an iPod would be a better choice than many other kinds of USB disks for the Zaurus, since it runs off of battery and can also be used as an MP3 player.