You can also make music with the iBook - one platform, for example, is Garageband, which is included in iLife 04. (For how to install Garageband on a clamshell, see the Installing iLife 04 tip). All that's missing for hobby musicians is an input device to record something.
USB keyboards can be bought for as little as 50 euros. When purchasing, ensure compatibility with the MAC OS, most keyboards are automatically recognized by the operating system without additional drivers.