Planning a trip to South America

I've been organising a trip to South America in July: Venezuela and Peru, flying into and out of Santiago de Chile. The Venezuela part (11 days) is being organised by the family of a friend, but I'm putting together the Peru part (another 11 days), tours to Cusco, Macchu Pichu, Arequipa, Colca Canyon. And all the air travel is up to me. I'll be flying on LAN, a Chilean airline. I wanted to book all my flights through the LAN website, so I can track and manage them online. Unfortunately, the website refused to process my credit card most of the time, despite getting it right once. Wanting to be sure to have the trans-Pacific flights locked in (just in case their very favourable business-class fares disappeared without warning), I fought my way through their telephone system to reach a human, who could only accept payment in US dollars... so I got stung with an extra card fee for that. Eventually I gave up trying to book the other flights and got a travel agent to do them, along with the tours I'd selected from the Tempo Holidays brochure. The Tempo website is hopeless.