There's a difference between taxes and retirement contributions. Income taxes you're probably not going to get back, and if you did, you'd immediately have to hand them over to the USofA. You need to find out if there is a tax agreement between the USA and Argentina -- someone on the board should know this and I know there have been NUMEROUS threads about US taxes. However your income tax is gone, you were resident here, so forget about it.
Pension and retirement benefits are separate. If you move to a country that has an agreement with Argentina, ie Spain, you can transfer these to that country. You don't get them back in your pocket, you just transfer them into the correlating program in that country. I know Spain has a programme with Argentina for doing this (my brother-in-law moved there and was able to take his pension/retirement contributions to their programme). I quite seriously doubt the USA has this, but again, you can find out. You need to find an accountant well versed in tax and pension funds -- and international funds. You will probably be best off contacting one of the big int'l accountancy firms -- ie Price Waterhouse Cooper, Deloitte, Ernst & Young who all have divisions here and in the USA and are probably more aware of what paperwork you will need. This could be quite expensive.
Most countries don't just give you back your income taxes when you leave. At the most if you're giving up residency you can get back your pension and retirement contributions. Being from Moldova you are I'm sure used to crazy government bureacracy. Trying to get your taxes back from Argentina is going to be an invite for the AFIP to examine all of your financials for the time you were here. You're going to have to go through his salary receipts and decide if this really is worth it. Also, there is absolutely no transparency from the government as to what is going on with the pension contributions, so what you see deducted from your salary receipt and what actually exists in the mythical account that the government supposedly has reserved just for you will not correlate whatsoever.