6 months doesn't seem long enough to do Central and south Aamerica justice, Where are you flying into?
Argentina is a beautiful country, make sure you go right down to the bottom of Patagonia. It's such an amazing place.
Chile is fairly expensive, the highlights being Torres Del Paine (spellling) probably the nicest place that I have ever been. San Pedro de Atacama in the very north is also pretty cool although very much different.
Bolivia is incredibly cheap and well worth a visit, there's not much to do in La Paz but it's a good craic if you stay in a good hostel with good people. Make sure you go to the north and do the joungle trek.
Bring lots of money and maybe concentrate and either central or south america
I think 6 months is plenty as long as you plan it properly. I got back from 3 months last week, did peru bolivia chile and argentina. Got stuck in cusco for a few weeks (watch out, happens to lots of people, always too hungover to leave!). Didnt make it to Patagonia, but i know lots of people there who have 3 months and get plenty of south america done. It is such an amazing continent. My favourite country is Bolivia, the people are all so friendly and its so cheap there. Try to stay in Loki hostel if you can, Osgur the manager is a Dub and hes sound out, they even have Barrys Tea! If you're planning on doing the Inca Trail book it in advance, it was grand when i was there in March cos it was the quiet season but by the time i was leaving it was booked up until the middle of May. I'm so jealous now, would love to go back, have a ball!!
Very good advice, thanks a mill. I'm flying into Argentina and hoping to take in Chile, Bolivia, Peru. We'll go to Brazil too if we can but we're flying out of Mexico City so we'll have to hit Central America in good time. Climate will impinge in terms of a route though. Would anyone have advice regarding a good route to take?