My next-door neighbor is Apple's developer responsible for writing communications drivers for Macs. I've asked hiom to play with PENG and Pronto. Although the software works mostly under Virtual PC, there are a few minor problems, and, as Peter pointed out, communications don't work. My neighbor says he suggested to Apple that he write a driver that would deal with Pronto, but apparently that is not a priority and they haven't green-lighted it.

No problem with Athlons. I have three Athlon-based machines, and it runs fine on all of them.