Three weeks is not a long time but get a few Spanish classes if you can, listen to Spanish music and watch Spanish language TV (thanks to the internet, this is pretty easy), especially from Argentina. Kids programs might be the way to go, or telenovelas. You can also check out "bueno, entonces" which is a download that teaches Argentine Spanish. Remember, Argentine Spanish is very different from other parts of Latin America, but practicing a bit now will make it much easier when you get here and give you confidence.
They estimate it takes two years to learn a new language if you study (in class and at home) and speak the language almost all day. A hard feat for most newcomers.