OK-
I received my undergrad here, and there are a few things to remember:
1) living in areas where schools are the primary focus is incredibly expensive. If you would like to live anywhere around Harvard, Northeastern (inc. the Harvard Med Campus), BU, or BC, you will pay AT LEAST $600 per bedroom. Living near those areas, or in areas that are easily accessible by the T, you can drastically cut down on the price of housing. My first two apartments near Northeastern cost me $600/mo. After learning the area, I moved to Jackson Sq. in Jamaica Plain, my first place cost $375/mo, bearing in mind that it was a three bed we converted to a four bed, my current apartment is $435/mo and is a very large 4 bed with hardwood floors, etc. right next door to my old apartment. It takes me about five minutes to walk to the Orange line, which equates to a ten minute commute to my old University. Of course, its quite a bit farther to Harvard, but more on that in a minute.
2) Public transportation here is pretty good. Harvard is on the Red Line, the 66, the 1, and several other bus lines, so getting there is little trouble from anywhere in either Boston or Cambridge. Forget about a car, particularly if youre going to try parking in Harvard Square, youre more likely to find bin Laden than a parking spot.
3) Ive seen a few posts about getting from BMC (Boston Medical Center/BU School of Medicine) to Harvard. The #1 stops right in front of BMC and will drop you off at Harvard ~30 mins later. I'm taking a class there and work in ID at BMC, so I do it regularly.
4) boston.craigslist.org. Use it at your own risk. There are a lot of college students (aka some students that prefer the bottle to the book), and there are a lot of horror stories out there. Try to make a relationship with someone here, or try to make a connection with someone who already lives in the area, this isn't a situation you want to go into blindly. I know a lot of people who've gone into roomate hunting with the "c'mon, I'm pretty easy going" mentality. When you're studying for your Consitutional Law final and 40 people walk through the door with 2 kegs, you'll throw your philosphy out the window like a politician does his wedding vows. Make absolutely sure those you're living with understand what you're trying to do and also have similar goals.
5) have fun. Boston's an amazing city for 20-somethings. It probably has the largest concentration of your demographic of any metro area in the world, enjoy it. Remember that part of what you'll have to go through is interviews, and just like a boring interviewee is never called back for a job, you have to be more than a brain, you have to have humanity, stories to tell, and the ability to connect with people from all backgrounds, and that's something that books can't give you, but the city can.
So there's my 2c. Boston's been a phenomenal city to me for the last 6 years, and I'm glad to call it home (and my employer). Anyway, I'll probably see some of you in the fall, best of luck.
-James