I have been reviewing some posts lately and I found it was completely necessary to update a few of them.
About Trains to Machu Picchu:
The first thing you must do upon arrival in Cusco is to buy the trains tickets to Machu Picchu. So, you should know that nowadays, there are two trains companies.
About Vegetarian Restaurants:
If you are vegetarian or just want to eat slightly, the city of Cusco has a variety of veggie restaurants (updated as of july 2013).
You should know that there are different rates depending on where you are from.