I am going on a cruise in Europe and have purchased Rail Europe train tickets - one from Rome to Civitavecchia, another from Le Havre to Paris. Is that a good way to go about?
Only if you don't care about the price. RailEurope adds their own commission to ticket prices. You can do better at the counter in Europe.
It may have been more prudent to ask if it's a good idea before purchasing. But in case you were planning to purchase any more tickets, the answer is NO, it's a better idea to purchase directly from the national rail websites or at the station. RailEurope marks up the ticket prices and also doesn't display all train times.