You didn't mention what your schedule was, but could you just wait and buy the tickets in Italy? At the train station? Those machines have always worked for me, and I've just used various US credit cards or Euros. Usually, I just buy the tickets when I'm ready to get on the train. If it is a long haul, and I need a particular schedule, I might buy them a day or two early.

When buying them while still in the US, you have to commit to specific trains, and sometimes your travel plans are not that definite. Plus, I think the tickets cost more when purchased here.

Romelle