That is mostly correct. In order for Windows to run on a PPC computer, Microsoft would have to recompile all of their software on a PPC processor, which is a large task. As you may know, processors only understand 1s & 0s, how the processor interprets the 1s & 0s is up to the designer of the chip. This is why Rosetta is needed to translate PPC instructions into an understandable form for Intel processors to run native PPC code.