Please read what I've wrote above: There ist no seperate callibration tool for G4-Macs, as you have seen for G5-Macs. G4-"calibration" is'nt such a sophisticated thing as on G5-computers.
I have no IBook, but I think there are also seperate tests for Sensors and fans (as on PB), which you can choose.
Please run the Sensor- and Fan-tests (click them seperatly - all other off). During running these tests, ASD-prog tries also to recalibrate!!
In most cases "fan-calibration" is OK, if all tests passed. If a test fails, you know what component is foulty and has to be replaced.