If I remember correctly, the iBook G4 has two USB 2.0 slots. However, I think that those slots might be under-powered. When I had a iBook I remember having problems with some USB-powered devices because they were not able to draw enough power from a single port.
The solution to your problem would probably be to get a double-USB cable. If you don't know what that is, it is essentially a cable with two plugs on one end and a single on the other, which allows the device you are attaching to the single-plug side to draw power from both USB slots. A lot of USB-hubs have cables like this to plug into the back of your computer so that they have enough power to run themselves as well as any attached devices. A google search should turn something up.