MacOS X: Self-assignet IP solution

Sometime my small MacBook G4 does not connect to the network and it always gets a self-assignet IP 🙁

Reset Open Firmware. As you turn on the machine, press & hold Cmd+Option+O+F until you get a screen that says “Welcome to Open Firmware”. At the prompt, enter “reset-nvram” (without the quotes). Press return. Enter “reset-all”. Press return and the machine will restart.
Open network preferences. In airport, go to advanced. Check the box that says disconnect the wireless network when logging out. (It seems incredible that it would work, but apparently it sometimes does.)
Restart in “Safe” mode (hold down “Shift” while restarting). Once in Safe mode simply restart again in regular mode. http://docs.info.apple.com/article.html?artnum=306879
Go into your keychain and find the password key for your network. If you connect to a WAP it will be the name of that WAP. Then in the key click on the access control tab. It probably shows selected applications. Change this to “Allow all applications to access this item”.
(The following apparently works temporarily, but it is not very clean. I would not recommend it except as a last resort.) Remove all the files and folders from the non-user Library/Preferences folder and reboot.