The kext development is really fantastic.

I am confused about the drivers though. Are they host processor dependent? In other words, if I am running 10.5.8 (the last Mac OS X that is supported on G4/G5) can I add some of the hack-supported hardware by using the same kext files even though I am on a G4?

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I just bought a $9- PCI wifi card on eBay (via Hong Kong) and it worked right out of the box on my G4 and so I ordered 10 more for our non-profit classroom environment. All the new cards do not work. The first card internally used a miniPCI board with a BCM 4306 Sagem ETS which just worked. The next batch have cryptically OEM's miniPCI WiFi boards on them: the MAC is 0012BFC6DFE8 (although that first 'B' might be an '8', which is either associated with: 00128F, Montilio or 0012BF, Arcadyan Technology Corporation).

I would really like to figure out if it possible to use a lot more of the modern hardware on the older PowerPC G4's since this work is opening up a lot of inexpensive hardware for uses like mine -- non profit classrooms, where we really appreciate the value of drivers for WiFi, USB, SATA/RAID, Tuner PCI cards, as well as Bluetooth, and other USB drivers

Can someone point me to an FAQ that explains if the KEXT code is tied to the host processor and how it works?

THANKS!

I can say that kexts must be exact the same arch as CPU. No Intel driver for PPC and vice versa.
But you still have possibility to take some hack-driver as they are mostly opensource and recompile it for PPC.
But some stones in the way: byte-order, physical addresses, and something else that I don't know. Clever PPC programmer needed.