FYI - a little known attribute of the W7 XP emulation mode is that it requires hdw support in the CPU - and not all CPUs (not even all Intel CPUs) have the feature.
Even if the CPU and version of W7 have the needed pieces, I suspect the PP driver may not run in XP emulation as it needs to manipulate real registers of real hardware, not an emulation.
Dave
I believe every version of Win7 has the XP emulation mode. You still can't run the Mach three driver with it though.