Windows is not PPC compatible in any way, shape or form so running it or booting a Windows disc on a G3, G4 or G5 Mac is impossible.
However, there are emulators out there like the old Virtual PC (ie: the one MS owns, but before they got it Connectix owned it). If the Microsoft versions don't work then you may or may not have more luck with the older Connectix versions.
You might have some luck with this, but I don't know how well the virtual machines can interact with the external hardware on the iBook. Apparently it's not blazingly fast either, but it's better than nothing. Good luck.
Edit: Noticed you said you've got 128MB in the iBook, I'm thinking that's a bit low... it's likely not gonna stop you running Virtual PC but it will very likely slow down the virtual machines a great deal, especially if you intend to boot XP in a VM. If you only need it for the one thing though it might still be worth a shot.