ken (BTW, nice name),
Yes, you can buy tickets at train stations in Italy using your Visa or M/C, either at the self serve ticket machines or at staffed ticket windows. Some of the automated ticket machines (especially in France and other countries) are being converted and will now only accept the "chip" credit cards, however when I was in Italy in June the magnetic strip cards were still useable at the machines. At the staffed ticket windows, magnetic strip cards are fine.
Where in Italy are you planning to travel? It's always a good idea to have some cash (even in a Money Belt) as some places "discourage" credit cards due to the fees. Some Hotels and B&B's will accept reservations by credit card, but require payment in Euros.
DON'T buy tickets in advance from Rail Europe as you'll pay more (sometimes considerably more). Buying tickets on the same day is usually fine, although I often like to buy tickets for an outgoing journey a day or two before I'll be travelling (especially where reserved seats are involved).
DON'T forget to validate tickets in the yellow machines before boarding the train!
For more detailed information on the automated ticket machines in Italy, have a look at Ron's website.
Happy travels!