There are 2 things that allow USB devices to work...
Drivers and a "host"
Dell Axim does not appear capable of "host" functionality even though the chipset supports it. It may just be a simple matter of decoding the pins on the bottom, but it might be much more than that.
PPC's have drivers for simple things like keyboard, mice, and ( soon ) mass storage devices.
http://www.aximsite.com/boards/showt...light=usb+host