See, the problem is not the fact that it is unsupported. Everybody should be aware that lots of people have gotten 8600s, 9600s, beige G3s, kangas, and all sorts of "unsupported" machines to run Mac OS X.
The problem is the 601 processor and NuBus architechture. Essentially, that makes it very unsupported - to the point of near impossibility (at least, it has been generally assumed by the Mac community until just now). In fact, the maker of XPostFacto clearly states that every machine with a 601 processor will not work, so do not even try.
Unlike 7500s and 8600s, where processor upgrades replace the original processor, the 6100 processor upgrade is an additional card. When you first start a 6100 with a processor upgrade, it still boots and runs on the original 601 processor until it is told "now it is time for you to use the G4."
Please, have your friend tell use how exactly he got OS X to boot with a 601 (which is very different an archaic in comparison to every PowerPC chip that followed). Also, tell us how he then proceeded to get OS X to run on a G4 in the PDS slot.
Those of us who know what we're talking about, are excitedly awaiting to be very amazed.