I use my Mac PB with the Hydra Nemesis 2.1x software all the time via Virtual PC. It's quite a bit slower than it runs on a native Windows environment, but it works pretty well with my 1.25 MHz G4. The key is to get a USB serial adaptor that has both Windows and Mac drivers. USB devices are notoriously hard to synch up with in VPC. Logging data is limited to 10 Hz, but a faster machine might get you to the Nemesis limit of 16 Hz, but 10 Hz is pretty good for road tuning in 4th gear.
If you search Macintosh AND Hydra you'll find my post in Tuning and EM forum.