Ok everyone! From hearing your comments on what to do about PV and doing some thinking, I came up with this plan of action:
Stage 1: Dependency - For now, everything references an installed version of Xenimus. During this period, PV will not charge a fee for anything (accepting donations only) and be clearly marked that it requires that Xenimus be downloaded to run.
Stage 2: Weaning - As we get more and more of our own content, begin distributing data along with the PV downloads. This will still require a copy of Xenimus to play, and will not charge a fee (again, only donations) but it will reference less of the Xenimus content.
Stage 3: Freedom! - PV is self-contained, using all of its own content and not requiring a copy of Xenimus. At this point, PV can charge a monthly fee to support itself and continue expansion of content/maps/etc.