Check out Kappy's user tip here > A Basic Guide for Migrating to Intel Macs from PowerPC G3, G4, and G5 Macs: Apple Support Communities
Might be corrupted network preferences ...
Open the Finder. From the Finder menu bar click Go > Go to Folder
Type of copy paste the following:
Click Go then move the SystemConfiguration folder to the Trash.
Restart your Mac.
A new SystemConfiguration folder will be re generated for you after restart.
message was edited by: cs
Might be something beyond Wi-Fi and Ethernet ...
Open System Preferences > Network > Assist Me > Diagnostics
If any of the buttons are red, click Continue.