I went to Buenos Aires for an internship in June 2012 for two months. It was my first trip flying solo and my first time in South America too! So yea I had nerves!
My host family was the best! They were the sweetest old couple and reminded me of my own grandparents :)
For one month I took spanish classes at Mundo Espanol and then for the second month I worked at a hostel.
At the hostel I worked Wednesday - Sunday from 8:30 am til 2:30 pm and I helped with serving breakfast in the mornings, and then in the afternoons I would assist the receptionist with reservations and promote day-to-day activities.
Overall I would definitely reccomend this for anyone who really wants to explore a new country or city and experience an amazing culture. I made lots of friends, had great memories and now I feel like it's my second home!