Pope Benedict XVI announced that he will resign at the end of February (read more on our Catholicism site). The conclave to select a new pope will convene in mid-March. This will most likely affect travelers in Rome who had plans to visit the Vatican, parts of which will be closed during the conclave (Sistine Chapel will definitely be off-limits although most parts of the Vatican Museums will be open), or to see the Pope at one of his Wednesday general audiences in March. Huge crowds are expected for the Pope's audiences in February.
Easter week is a very popular time to visit Vatican City with the Pope normally saying Palm Sunday mass in Saint Peter's Square to start the week and leading the Good Friday Via Crucis near Rome's Colosseum. At this time, it's not certain how these events will proceed but we'll update whenever new information is available.
Photo of Pope Benedict XVI on Palm Sunday by Doug Baumgart, used by permission