Yes, I recently changed the hard drive in my iBook.
This Guide will show you how to open up the iBook enough in order to get to the drive. Make sure you label the screws (wrap them in tape and tape them to a piece of paper listing where they came from), although this is not so important if the iBook is dead, but you may want to put it on eBay for spares.
You will need a FireWire (or USB 2) enclosure for the disk. It needs to hold a 2.5" disk rather than the standard desktop 3.5" disk. I have a few FireLite enclosures from
SmartDisk which I put disks into (they only sell them with disks already in on their website), but you can probably pick up an empty enclosure at an online store, if not eBay.
My advice would be to get a firewire enclosure (remember it is 2.5 inch) as it can run on power from the iBook and doesn't need an adaptor.
Anyone else know of any good enclosures/places to buy them?