Before I even get to my itinerary, let me first agree with all your replies that the time we have is too short to see much! We'd still like to fit in as much as possible as this is a once in a lifetime trip to the continent. Our other challenge is the weather, as we plan to visit June end-July. So far we have just a bunch of places we've 'narrowed' it down to:
1. Machu Pichu
2. Iguazu falls
3. Salta (or any wine region that fits in better logistically)
4. Either Bolivia or Rio

We definitely want to visit at least 2 countries and maybe a third as again, this trip may not happen for a long time (from India).
Considering that it is winter, which of these is a good idea? How should we route the trip?

We are a group of generally well traveled 30 year olds (all couples); we're reasonably fit, enjoy good food (all of us are vegetarian) and wine but don't speak any Spanish We love quaint little towns, aren't really looking to rough it out, wouldn't mind some history for a short time, would enjoy some nightlife and are looking forward to some spectacular scenery along the way.

Any help would be appreciated!
Thanks!

I'm only able to give you feedback for Peru. The summer is the best time to visit Machu Picchu weather-wise, but this site tends to get quite crowded in the summer months. Keep in mind that you need a ticket to get to Machu Picchu and you must schedule in advance.

While you're in Peru you could also visit the coast and see the vineyard that grow in Ica. They make some wine as well as Pisco, a type of Peruvian brandy made out of grapes. Ica is about 14+ hours from Machu Picchu/Cusco by car, but I thought I'd throw it out there since you're also thinking about going to Argentina's wine country.

Good luck with planning the rest of your trip!

Yes you are trying to pack to much in to the time available. That is entirely your prerogative, but I would strongly suggest you do more research yourself before asking for specific help here. Start by looking at a map/ South America guidebook and a website like kayak.com where you will be able to ascertain the viability/logistics of getting around South America which is not always straightforward, especially if you are in a rush. There are also many tour company websites which have many "today is Tuesday, this must be Machu Picchu" pre-planned tours. Intrepid travel is a good starting point.

June - July is generally a good time to visit most of the places you mention but you do need to be prepared for the weather in terms of warm clothes etc.

A general itinerary, which has been well trodden by others might be:

Lima
Cusco - for the Sacred Valley and MP
Puno - Lake Titicaca
La Paz
Salar de Uyuni
Salta - via Tupiza
Iguazu
Rio or Buenos Airies

This route would involve some expensive flights and very long bus journeys

Could this be done in two weeks? Yes.
Should it be done in two weeks? No.

Seriously, I would think again. You could easily spend the whole two weeks in Peru and be blown away by the scenery, the food, the scenery, the history and, indeed, the whole experience. The wine is awful but you can't have everything

Good Luck! You will need it!