The first thing that I would do would be to get an extension on your 90 day visa limit stay in the country once you arrive. It's pretty cumbersome process to get a work visa here, and you might need all the time you can get to get one. Moreover, I would also look into getting a student visa which is also an alternative for prolonging your stay... But you could always teach English here. I would recomend looking into the O Globo (newspaper journal) sunday "boa chance," where you'll find some work opps. But you get also look into this Brazilinan site for ngo and other types of work. arruda.rits.org.br/notitia1...etDeSecao
Go to the "oportunidades" selection on the left hand side to see newly posted jobs.
Learning portuguese helps a lot too! I live in Rio right now and you can give me a shout when you get in. peace