Update March 7, 2008
Dartmouth's residential life office is looking at buying several properties, two of which might be used as housing for Alpha Xi Delta and Alpha Phi. Article is at:
http://thedartmouth.com/2008/03/07/news/orl/
By the way, the article hints that there may be interest in adding another NPC sorority in a year or so. This doesn't mean that it'll happen, and AFAIK there's been no announcement that the school is open for NPC expansion. We'll see, I guess.