I can confirm that you do NOT have to leave the country in order to get a student visa after entering on a tourist visa (I think the law was changed several years ago). I did this in 2007 (and I was even part of a program). KatherineAnn- I brought along the letter from the police station and everything but they didn't even use it or ask me for it. When I actually received my visa all I had was my passport and copies and the Buenos Aires police letter. That could be due to the fact that I was part of a program, but who knows. Certainly, the letter from your local station and the apostille authentication will work.