Hi Brumiga!
Apple Service Diagnostic (ASD) software is/was only distributed to service providers for repair and maintenance of apple machines. So it's not really a public software... Obviously it's possible to obtain it in a certain way.. though it is really hard!
Moreover one has to use the appropriate disk for his own system.
Here a (brief)list concerning G4 and G5 machines:

Dual Boot 2.1.5 (2003)
PowerBook G4 (12-inch), PowerBook G4 (17-inch), iMac (17-inch 1GHz), Power Mac G4 (FW 800), Xserve (slot load), eMac (ATI Graphics), and Power Mac G4 (Mirrored Drive Doors 2003), iMac (USB 2.0), PowerBook G4 (15-inch FW800), PowerBook G4 (17-inch 1.33GHz) and PowerBook G4 (12-inch DVD)

ASD 2.5.7
PowerBook G4 (17-inch 1.5GHz), PowerBook G4 (17-inch 1.67GHz), PowerBook G4 (15-inch 1.5/1.33GHz), PowerBook G4 (15-inch 1.67/1.5GHz), PowerBook G4 (12-inch 1.33GHz), PowerBook G4 (12-inch 1.5GHz), iBook G4 (Early 2004), iBook G4 (14-inch Early 2004), eMac (USB2.0), Power Mac G5, Power Mac G5 (June 2004 Series), Power Mac G5 (Late 2004), Power Mac G5 (Early 2005), iMac G5, iBook G4 (12-inch Late 2004), iBook G4 (14-inch Late 2004), Mac mini, and iMac G5 w/ALS (Ambient Light Sensor)

ASD Dual Boot 2.6.3
PowerBook G4 (17-inch 1.5GHz), PowerBook G4 (17-inch 1.67GHz), PowerBook G4 (15-inch 1.5/1.33GHz), PowerBook G4 (15-inch 1.67/1.5GHz), PowerBook G4 (12-inch 1.33GHz), PowerBook G4 (12-inch 1.5GHz), iBook G4 (Early 2004), iBook G4 (14-inch Early 2004), eMac (USB 2.0), Power Mac G5, Power Mac G5 (June 2004 Series), Power Mac G5 (Late 2004), Power Mac G5 (Early 2005), iMac G5, iBook G4 (12-inch Late 2004), iBook G4 (14-inch Late 2004), Mac mini, and iMac G5 w/ALS (Ambient Light Sensor

So it's not necessary to have all disks but only the one you need.