Airports, São Paulo

Most of the international airlines have a 'pit stop' in Sao Paulo, before going to Rio de Janeiro. I would consider a 'stop over' if possible with your ticket. But you need at least 3 - 4 days to explore the city. Driving from Rio (which I did) takes about 4 - 4,5 ours. The roads are great, but there is a lot of traffic.
You have the Metro. Otherwise; why dont rent a car? The signs and the roads make it surprisengly easy to find your way (if you know where you going...). See my Rio pages for more info about car rental.

Use airplanes!
Travel by companies such as TAM, Varig, Vasp, etc
Don't rent cars, traffic is terrible and, unless you have a native to drive you around you will get probably get lost(streets and avenues don't follow a pattern like New York)
Use the subway, taxis and buses.

For air travel, one can't beat the convenience of Guarulhos International Airport (GRU). See oncierge.com for more information. Unfortunately, there is no official web page for the airport.
From GRU, one can take a shuttle bus to pretty much any part of the city or surrounding suburbs. Here's a picture looking out from the airport exit at the bus stop.

They may not be 777s anymore, but UA does have wonderful non-stop DAILY 767 service to GRU Sao Paulo from IAD (Washington-Dulles,) and ORD (Chicago O'Hare.)

The main airlines arrives at Guarulhos Int. Airport (GRU).
Bus and Metro, are easy to use. Take all information you need at Information desk at airport.