Reading code from array efficiently
Sure,

you are basically copy pasting to keep accessing arTab and promilleTab, you might instead just derive the indexes in arTab from bruddListe and arListe, like this:

function skrivUt(Event:MouseEvent)
{
  txtSvar.text = "I " + arTab[bruddListe-1][arListe-1] + " ble det anmeldt " + promilleTab[bruddListe-1][arListe-1] + " for promillekjøring";

etc. etc.


or you could keep things a bit more readable, by splitting it up, I dont know if this is correct ActionScript, but conceptually you should grok this:

function skrivUt(Event:MouseEvent)
{
  var ar:String =  arTab[bruddListe-1][arListe-1];
  var promille:String = promilleTab[bruddListe-1][arListe-1];
  txtSvar.text = "I " + ar + " ble det anmeldt " + promille + " for promillekjøring";


Furthermore, some other observations : 


Try to keep your variables and function Names in English, it's the right thing to do
it seems as if bruddListe and arListe are global variables, you should avoid those