A note on Appleis support Web site says "because of its design, iPod shuffle cannot be connected to the USB ports on the side of iMac G3 and eMac computers ? it will not fit (because of recessed or closely spaced USB ports). You can connect iPod shuffle to your keyboardis USB ports if your computer has Mac OS X 10.3.6 or later, however, iPod shuffle will not charge due to the keyboardis low-power USB ports."
All is not lost in using the shuffle on these older Macs. Users can either use the iPod shuffle Dock or a third-party USB extension device, and must be connected either directly to the USB port on the CPU or to a high-powered USB port on newer keyboards.
Macworld UK was the first report this incompatability.