Is it true that you only need a Passport and not a Visa to enter all Central and South American countries?

You should be fine for the most part. Most countries don't require a visa, but rather a "tourist card" that roughly costs $10 or so. This suffices instead of the visa. There may also be a departure tax depending on your method of departure when you reach the border. I would advise that you check out the Immigration Departments of the countries you are visiting just to make sure and learn about specific requirements that there are for New Zealand citizens. Brazil may be a country you need a visa for, but don't quote me on that. Your best bet is to check out their immigration website and find out. Argentina requires a visa for American citizens upon arrival, and that's about $100. This could vary for you as a NZ citizen.

For the most part, you won't need a visa, just a tourist card. However, I strongly suggest that you check with each individual country before you travel. Use google translator if you have to, but please do check thoroughly. You don't want to be stuck at an airport or at a border crossing, or worse, locked up in prison for a small misdemeanor that could have been avoided all together.

Happy travels!

I cannot speak for South American, but in Central American countries a New Zealand citizen has to have a passport valid for at least six months and proof of ongoing or return travel to be issued a thirty day visitor visa upon arrival. That visa can be extended for up to ninety days if you make application before it expires.

Almost true.

Where are you going exactly? Most country won't require a Tourist Visa to NZ citizens.

I'm not sure if this is 100% true considering how whenever my family travels from Venezuela to Colombia they ask for a visa.