McGarry is right, the topic of iBook vs PowerBook has been covered many times before. Try this recent thread for a few hours of reading. It covers just about everything you need to know (and we probably don't need to go through it again):
https://forums.macrumors.com/threads/100581/
Very briefly, comparing 12" iBook to 12" PowerBook, the differences are:
- Slightly faster CPU and bus speed in the PowerBook (1.33GHz vs 1.2GHz CPU speeds, 167MHz vs 133MHz bus speeds).
- Larger video RAM in the PowerBook (64MB vs 32MB).
- nVidia FX5200 Go GPU in the PowerBook instead of a Radeon 9200 Mobility in the iBook (the nVidia FX 5200 is supported by CoreImage, but in reality neither GPU is particularly impressive for 3D/gaming work).
- DVI video output in PowerBook instead of VGA in iBook.
- Built-in display spanning in PowerBook instead of display mirroring only in iBook (but this can easily be added to iBook by an unsupported firmware modification).
- Audio-in jack on PowerBook, no audio-in jack on iBook (but cheaply solved by a USB line-in adapter).
- Superdrive option available on PowerBook, Combo drive only available on 12" iBook.
- PowerBook marginally smaller and lighter than iBook.
- iBook case materials reportedly more robust and damage-proof than PowerBook case materials.
- iBook battery life reportedly better than PowerBook battery life.
- iBook and PowerBook aesthetic appearances obviously different and will appeal differently to different users.
Of course, the biggest difference is the price, which falls heavily in favour of the iBook. If you don't need some or all of the features the 12" PowerBook adds over the 12" iBook, then it's a pretty poor value proposition. Get an iBook instead. However, if you need the features, then the PowerBook wins. It's a personal decision in the end.