Yeah, the PS codebase comes with enough art to run a particular area, from there you can just patch in your own maps and content. I've personally done some work on an Ancient Greek mod for PS. Given the amount of work involved in making the art part of a game, especially to a competent level, there have yet to be any PS-engine open source alternatives made available, due to the fact they're simply not to a releasable level of quality.
