The hack I use is called screen spanning doctor, download here:

Works great and I have been using it for over a year without any problems on my 1.2ghz iBook G4. Avoid the Clamshell option it offers you, While others may differ I would not reccomend running the iBook with the lid closed.
PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...