If you want to write Anders Behring Breivik in prison your letter should be addressed to:
Anders Behring Breivik
Make sure to change Norway in the address to the proper translation of Norway in your country’s language. The Norwegian prison authorities will confiscate all monetary gifts to Anders Behring Breivik, most likely to place these in a fund that will be used to pay money damages, as to be determined in court. In short, only send money if you want to donate to category B and C traitors.
As such Commander Breivik is unlikely to respond due to insufficient funds as he has to buy his own stamps in prison, meaning you have to include a 15 kroner stamp for intercontinental postage, 13 kroner for European postage, and 10 kroner for Norwegian postage. Thirteen Norwegian kroner is the equivalent of (roughly) two Euros.
Obtaining Norwegian stamps is somewhat tricky. The Norwegian postal service has an English version of its website, but the section dealing with the ordering of stamps is broken.
In the likely case that link doesn’t work you’ll have to make your way through the Norwegian section with a little help from Google translate.
As should be obvious, all letters are read by the Norwegian prison authorities.