Probably the best thing a single person could do to help speed up the development of PS is to spread the word, why dont you visit something like deviant art, do a search for 'medieval' under '3D digital art' and put a nice little comment on any interesting/applicable works.. its amazing how many collage students are looking to expand their portfolio for a resume...

write something along the lines of ...

"Nice job! i see you've got a good eye for detail... if your looking to expand your range of experiences (perhaps to expand your portfolio or whatever) might you consider contributing to the development of an open source mmorpg? if so, visit (www.planeshift.it)"

it works like a charm

Maybe out of 10 comments you may get 4 or so people willing to help out, and out of them maybe only one person who's in it for the long run, but for that little effort you've helped planeshift a lot!