First you should download the Jaman Player. You can download it from:
http://www.jaman.com/a/download/?theAction=show_download_client
Make sure you read the minimum system requirements and that your computer meets these minimums. Then find a movie you are interested in. If the movie is not available in your country, you'll not be able to download it.
You can click on the browse tab and choose "available in my country" on the left hand side of the page. Then as you browse, you'll only see movies available in Argentina. Once you find one, just click "I want it" on the movie's detail page. Do all of this from inside the Jaman Player, and you'll be downloading and watching in no time.
Jaman Jamie