If your iBook does not have the AirPort Card installed, the antenna cable needs to be secured to ensure it does not come in contact with the logic board. Such contact could damage the iBook logic board.
Refer to Figure 1 for placement of the antenna cable under the wire bracket.
Figure 1 Placement of AirPort Card Antenna Cable
Note: Wireless Internet access requires an Internet service provider (fees may apply) and AirPort (or AirPort-compatible) wireless Ethernet card and base station. Some ISPs are not compatible with AirPort. For more information, see technical document 106590: "AirPort: Requirements for Wireless Internet Access"