UK v. US RailEurope
 

As a US resident, will I be able to buy the tickets off the UK website? If they need the mailing address to be in the UK, then that wouldn't be a problem since I have a friend who lives there.

yes, no problems.

they don't care where you come from.

What tickets are you intending to buy?

Thanks for the replies. I'm planning to buy tickets for the night train from Munich to Venice on May 28th and Rome to Paris on June 1st.

Then book the Munich-Venice segment using www.bahn.de and the Rome-Paris section on www.trenitalia.com, thus avoiding the markups that Rail Europe charges.