Version 2.0.1 is the proper Apple Hardware Test for the MDD G4 with FireWire 800. There is another version that says it works on the MDD, but that's only for the non-FireWire 800 version. Very confusing.

Here's a download link from Apple for AHT 2.0.1:

http://download.info.apple.com/Apple_Hardware_Test/693-4817-A.dmg

This is the one we want to play with - the only disc that sorta boots OS 9 on this Mac.