I assume you mean Isernia?
Were you thinking of driving? If so know that Romans can be considered pretty crazy drivers. What we might call "reckless." They're good at what they do, but unfortunately there are other people on the road who might not be as in tune with the unwritten rules of Italian roads.
If you're not interested in that adventure, train travel is your best bet.
Trenitalia.com is the main provider and you'll find tickets around $15 for a 2-3 hour trip...about the same time spent if you were driving yourself. That's the route I would take.
If you choose train travel, please read up on some of the safety tips on the Termini in Rome (main train terminal). Crime can hit you if you aren't paying attention to your surroundings. Keep your money in a safe place and keep your eye on your luggage at all times.