Of course any Israeli (except peace activists) you ask will tell you that it's too dangerous to go to the Occupied Territories, but I've traveled there lots and it's definitely feasible. You can contact these people: http://www.toursinenglish.com/. Their tours are more geared towards education about the occupation, but I'm sure that if you emailed them they could tell you how to get to the spots you want to go specifically. They DO go to Nablus. Like I said, though, their tours are geared towards education on the occupation but if you want to go there it's probably the easiest and safest way. I went to Nablus last year, but with a Palestinian friend, so I don't have experience booking with the tours, though a friend of mine went on one and enjoyed.