I just graduated from UMass Amherst and have accepted a job in a NICU in washington dc!
As far as a preceptorship in the NICU at Amherst, I know only one person who was able to get one and she commuted to Boston for that to Brigham and Women's. I had my preceptorship on a pedi floor at Baystate medical and it was wonderful, during my pedi rotation there I did spend some time in the NICU, keep in mind that preceptorships are competitive and you have to really show why you are interested in a specialty...and then keep bugging the professors to get what you want, if you make the effort in the early years to get to know your professors and establish relationships with them then they will do everything possible to help you succeed.
As I said, I just graduated UMass Amherst, I have a friend also in the nursing program at UMass Dartmouth, she has one more year. I have heard horror stories from her about unfair professors, clinical instructors and exams as well as professors who just don't seem to want their students to succeed. I have told her my own stories about my professors who make sure every student has their cell phone number in case of an after hours studying emergency, professors who will meet with you on a Sunday evening to go over an exam if that is the absolutely only time you can meet. I sat down for an hour with one of my professors after graduation to make a complete day by day study guide for the NCLEX based on my individual testing results...this professor also happened to write her own NCLEX review book and offer a semester long optional NCLEX prep course for us. My class was very small, with only 65 students, we took all our classes together from sophomore year on, I knew every person in my class, had most of their cell phone numbers or screen names and always had someone to call if I had a question on homework or needed someone to study with.
Another plus, this past year we they just opened a brand new nursing building with state of the art Sim men (I don't think UMD has those) on which you can practice almost every nursing skill needed to know. This building also has study areas, computer rooms and easy access to all the nursing faculty and professors in one place. UMass Amherst also has a BEAUTIFUL campus in one of the most beautiful parts of Mass if you happen to like the outdoors and being active.
As far as getting into the program the system has changed a little from when I was accepted, I had an EXTREMELY competitive class with the top 25% of our class having a 3.8gpa (college) or higher. I know that if you do not get into the program out of high school you cannot go to UMass undeclared and transfer in, they will not take transfers (I believe UMD will take transfers) I am not sure what the high school gpa acceptance is because when I applied the process was very different from what it is now but I think you can look at the website for that kind of info (www.umass.edu/nursing
As far as overall program satisfication I LOVED my experience, I was also a member of the varsity D1 rowing team and had many schedule conflicts between practices, races, clinical and classes and most of my professors were more than happy to help me compromise and do everything I wanted to do.
Good luck with your remaining high school years....they will be over before you know it, definitely if you get a chance, visit both schools and talk to nursing students from both to get a feel for each. UMass Amherst though was perfect for me :-)