3 days in Rome, 3 days in Venice, one day on trains.
Rome: 1 day in Vatican, 1 day for Forum and Colosseum
Venice can be 2 days or 3: 1 day for the main sights, St. Mark's Square and Rialto Bridge, another day just walking around, taking in the view. If you have a 3rd day, go to Murano and/or Lido.
And a shameless plug for my own Rome vacations photos, :)
罗马假日