I use my old PowerBooks for simple webradio & iTunes audio playback. I also use my PowerBook G4 17" 1,67 Ghz for my canon flatbed scanner since canon stopped to update the driver after Tiger...
I will probably use my two old PB G4's once I decide to convert my library of CD's (in ALAC-form) to the more portable AAC. It takes a while but keeps my main mac free and ready to use for other stuff.
(but otherwise it almost starts getting to be a problem, my macs just keeps spinning and my collection of old, used & a bit slow but still mainly functioning macs just keeps growing... Got 6 macs right now.)
The Core Duo MacBook can run up to Snow Leopard. If you throw 2 GB of RAM in it and a good SATA SSD it will run great. It will be a fine machine for basic usage.
The PowerMac/Book is good for basic work that does not involve the internet. If you need it for the web then I recommend TenFourFox or Leopard WebKit. If this is a PowerBook as in laptop, and you don't want it anymore I will take it off your hands for fair market value. PM me if you want to get rid of it.