Snow Leopard will not run on PPC (at least that is my understanding).
I'm confused, I thought one of the complaints about Vista was the fact that it would not run on older hardware.
Isn't that pretty much what I said? Vista was the whipping boy MS needed to make a break with much of the legacy equipment. Still, Win 7 will run on many computers that Vista wouldn't-couldn't because it has a smaller footprint(one guy on the
Win 7 forums has it running on a laptop with only 500MB of memory and an old x86 cpu).
In most cases the failure has more to do with the lack of suitable drivers for that legacy equipment. Many vid cards would be capable of running the software if their manufacturers would provide updated drivers. AMD/ATI for example is unlikely to provide video drivers for older video cards (like the X series) for the newer operating systems (I have a set of crossfired Radeon X1650's in one of my older computers that are fully capable of running Win 7-separately or jointly-but the driver support is not there).
Most legacy problems can be attributed to driver problems. It's understandable; why continue to support a 5 year old card when you can force people to buy a newer one?
It is that broad flexibility and wide selection of suitable hardware that allows Windows to so dominate the market. Apple marginalized itself when it chose to remain a closed system (you must buy your computer from Apple) though that has changed, with questionable legality, with the advent of "hackintosh" computers.