Yeah, we need to get a handle on what machine you're talking about. iBook G4 from 2009 -- not possible. G4s were LONG gone by then, iBooks stopped in 2005 as Nick says.
Go to "About this Mac" (first item under the Apple menu) and let us know what you ACTUALLY have.
PS. Regardless, all iBooks ever made (and all MacBooks ever made) have Wi-Fi. The really old machines (iBooks) don't support more than 802.11g and certain levels of security, so your actual problem might lie in that area somewhere.
1. As member Chas_m suggests the wireless access point you are connecting to may be using WPA/WPA2 as a form of security and your iBook cannot handle that level of encryption. I ran into this with my own iBook several years ago when I changed the security settings on our home network.
2. The network settings on the computer are incorrect (WEP/WPA issues again)
3. Failure of the wireless card. Less likely but possible given the age of those machines.