Reading this it sounds like Person Accounts are incompatible with the Non-Profit Starter Pack, which is totally understandable. What I am having trouble finding is a direct answer to whether it is still possible to install the Non-Profit Starter Pack into an org with Person Accounts as long as you don't use that record type any longer (since it isn't possible to turn Person Accounts off).
Is it possible to have both enabled in the system, or does moving to the Non-Profit Starter Pack require a new organization?