1. Plug the power adapter in and fully charge your computer's battery until the battery indicator lights turn off and the adapter plug ring goes from amber to green, which indicates that the battery is fully charged.
2. Disconnect the power adapter and use your iBook or PowerBook. When your battery gets low, you will see the low battery warning dialog on the screen. Continue to use your computer until it goes to sleep. At that point the battery has been sufficiently drained for calibration.
3. Connect the power adapter and leave it connected until the battery is fully charged again.
I think one has to folow a similar procedure with the iPod too. On first use Apple also recommends draining to sleep then charging to full.
When an iBook or iPod really loses its battery calibration, one may need to do a reset (standard reset on iPod, PMU reset on iBook) after plugging in the discharged device.