how can I install window os on my mac IBook G4?

On an iBook G4, you're better off buying Microsoft Office 2004 or 2008 instead of attempting to run Windows on the computer; if you really want to run Windows on a PowerPC Mac, your options are very limited, but include Virtual PC and the Q emulator.

(103049)

https://discussions.apple.com/docs/DOC-2741

say more about what's available for PowerPC Macs. Under emulation all audio and video is too slow.

See my FAQ* about alternatives for Microsoft Office:

http://www.macmaps.com/crossplatform.html

Some have been made for PowerPC Macs.