iBook G3 connects to wifi but not Internet

The iBook G3 is only capable of 802.11b WEP encrypted or WPA1 encrypted WiFi. This is very insecure, and it is possible your settings either changed, or your WiFi connection isn't sending the right data over. You are better off connecting to the WiFi router by ethernet to its LAN port, or getting a WiFi ethernet bridge for the connection that supports 802.11g or later with WPA2. Not to mention your wireless connection slows down to 11 Mbps or less because that's the top WiFi speed the iBook G3 supports. You might also want to upgrade to 10.4.11 using this link:

Mac OS X 10.4.11 Combo Update (PPC)

As that version of 10.4 has the best wireless support of all.

Also of note...

The Interface that connects to the Internet, needs to be drug to the top of System Preferences>Network>Show:>Network Port Configurations and checked ON.