I had a nice long email chat with members of the Virtual PC team.

The good news:  The Virtual PC emulates the host processor well enough that our kernel-mode driver can detect what features are enabled.

The bad news:  The Virtual PC does not emulate an APIC or performance counters.

So, if you were planning on running the profiler inside a Virtual PC, the best you can hope to do is get function trace data on an instrumented app.  Sampling will not work at all, and collecting perfomance counter data in the instrumentation will fault the application.

Bummer.  I wish I had better news.