Hi! I'm glad to see someone's posted for UMass. I'm attending in the fall, as well, but as a Master's student in the English department. Actually, I'm from Massachusetts and my brother attended UMass for undergrad, so I know that usually students start looking for apartments in the spring time. I found my place through the off campus housing site. Also, I know that, for the years he lived there, my brother's one year leases would start at the beginning of the summer (as in: from June to June) and he would sublet out to someone for the months he didn't live in Amherst. Realtors will sometimes offer to help with that, as well, but if you're like me, you'll probably be avoiding realtors at all costs.
Also, I'll let you know: I'm not a pro with the area, but I've heard from multiple sources that Northampton is a really fun place to live. I drove through the downtown area and it was really cute! I saw a cool looking music venue, and I've been told that it's "hip and laid back," if that's what you're looking for! My place that I'm staying is in a neat neighborhood in Northampton and I'm very excited about it!