Powerbook 12" 100% CPU

Hmm that's odd. The powerbook G4 should handle itunes with ease. Have you tried reinstalling it?

 

This is not typical behavior and doesn't have anything to do with your particular computer (it's got more than enough to run OS X).

I would try this:

Make sure iTunes is closed. Go to your home folder (the one with you name), then to "Library", then to "Preferences", delete the file: com.apple.iTunes.plist and empty the trash. Now, go to your "Applications" folder, then to "Utilities" and run the "Disk Utility". Click on your "Macintosh HD" on the left and click "Repair Permissions". Once complete, restart the computer. Now, open iTunes and go into the Preferences for iTunes. Turn off Library Sharing, and search for Shared libraries. Turn Podcast "check for new episodes" to "Manual". Turn off search for Apple TV. Close iTunes. Re-open iTunes.

Let me know if that worked, if not, come back and we'll try something else.