Thanks to help here I've chosen to fly LAN, Sydney-Auckland-Santiago, then Santiago-Sao Paulo. It was suggested by the travel agent that I could have 45 minutes between flights at Santiago.

This seemed awfully tight to me (last time I had a connection this tight I made the flight but my bag didn't). Anyway, I've opted for much longer between flights, but was wondering if 45 minutes really is sufficient for an international connection?

I've not travelled through Santiago International Airport but no matter - 45 minutes is too short of a connecting time betwenn any international flight - just about anywhere in the world. There's simply not enough time for you to clear immigration, claim your luggage and clear customs (and security, if necessary), re-check your bags, get to your departure gate and board your outbound flight. You can do 45 minutes (at the minimum) for a domestic to domestic flight but for international connections you would be just asking for trouble. Remember, Murphy's Law of airports states the shorter your connecting time between flights, the greater the chance your in-bound flight will be delayed, the longer the lines will be at immigration and customs, the longer it takes for your baggages to be off loaded and the further you will be away from you departure gate.

I think its too short. I changed planes in Santiago last summer and recall a long walk once off the plane then a line thru security/immigration that took a good 40 minutes.

You shouldn't have to pass through immigration and customs since you are not staying in Chile, so that time-consuming task shouldn't enter into it. You will be able to go right to your gate for the connecting flight. But I think 45 minutes is still too tight for a connection. If you incoming flight is late, you'll miss your flight to Sao Paulo.

Jeff's right about not having to clear customs/immigration as you'll be "in-transit". I had monemtary brain fade and didn't focus on the fact that you were flying on to Sao-Paulo and not some other city in Chile. Sorry for the mis-information but 45 minutes is still a rather short connection time (anywhere).

Thanks very much for your help, I now have a 5 hour gap between flights. A bit long, but I think better to be safe than sorry.

Obviously Jeff has never changed planes in Santiago. When you change planes you wait in line to go through security (xrays etc) before being allowed into the main terminal to board your connecting flight.

Thanks jpg2esq, that makes 45 minutes even less likely. The TA kept insisting it was possible, but I really wasn't convinced.

Sure I have, but they have always been international to domestic. I recall (but could be wrong) that the passengers on the flight from Miami who were connecting to another international destination in Santiago were shunted off to another international gate to wait for their flights. And that gate was right there within walking distance.