Sandra, I am studying at UBA. I studied once for a full semester and now I am doing a full program. The first time I only needed the "mini" student visa as I will call it without all the full blown paperwork and now I am getting the real, full blown student visa!
If you haven't left the States, right away, get your FBI paperwork sent off (it's just a fingerprint card your local police can help you do and a "cover letter" form). It will be MUCH faster that way; it's min 13 weeks for the FBI to process it I found out...and they won't even tell you in FBI customer service it's arrived until after 10 weeks from receipt. Mine FINALLY made it to my parents' house this week when I sent off for it from Argentina the last week of March and still has to go out for the Apostille from the US Department of State. Make sure to request the signature of an FBI official for the purposes of getting an Apostille seal; otherwise the US Dept of State won't Apostille it.
http://www.fbi.gov/hq/cjisd/fprequest.htm
Make sure you also have your Apostilled birth certificate, which you can get on a trip to your state's capital city if you don't have it in hand yet. You can also do that through the mail most likely from Argentina if you absolutely must. But make sure to mail any precious necessary documents by certified mail because I already lost one of mine in the mail along with precious time.
You will be fine. You could apply for the TWO different kinds of student visas if you want to be legal in the short term (i.e. tourist visa to mini student visa upgraded to full blown student visa)--but then you would have to pay the 200 pesos plus other costs of transmites two times, so why do that?
My university advised me as long as I stay in the country while I am getting my paperwork for my student visa done, I should be fine. While they are not immigration, I have already overstayed a visa twice here and paid the fees upon leaving the country, so I know they are right.
Check the warnings on here about apartments, particularly individuals renting and keeping your deposit. I have never had a problem, but there are a lot of wise individuals on here who have lived through some challenging rental experiences and have good advice to give.
And I will say again if you are a biker, bring a nice bike used lock so you can buy a used crap bike on Mercadolibre for 50 bucks when you get here...in 2.5 months you will make up the difference in bus/subte fare that way and it's well worth it to explore the city. I can park mine INSIDE the college building's courtyard.
