Hey Bugger,
I've taken the train from Cusco to Titicaca and its a fantasic ride with plenty of stops in towns. The tracks a bit old but it all added to the character. Here's the
Train Cusco to Puno stopped for a break. Here's the
Train Route and Booking information Cruz del Sur has bus service from Cuzco to Puno and it takes 6 hours.
I personally enjoyed the train ride and would recommend this over the bus for the experience.