I know this may not be what VPCers want to hear, but I strongly suggest laying out a roadmap for yourself for abandoning VPC. It will not be updated again, and generally speaking it is only a matter of time before using an EOLed product becomes very inconvenient to operate and keep running. Nobody tests things like OS upgrades with obsolete products, and support for obsolete products inevitably dwindles at various speeds. If you count on Windows, you need a better solution.
It is so easy to build a super cheap PC for running Windows that I would suggest doing this and using the Microsoft Remote Desktop protocol if you do not need to run Vista. Doing so is much faster and more convenient, IMHO. If this is simply not an option, I would suggest checking out Qemu, it might work on PPC hardware.