CO flies to Santiago via Lima from EWR and IAH. There are frequent connections between Santiago and Buenos Aires on Lan Chile and Aerolinas Argentinas (and AA may still fly a daily route as well - they did two years ago at least). Problem with the Santiago flight is that it usually arrives in Lima in the dead of night (I think). The only benefit is that if you get a left side window seat you will see one of the most amazing sunrises (over the Andes as the plane is descending) ever.