[Хрюндик]

//init part(add to the first frame!)
max = 26;//number
used = [];
//main part
number = random(max)+1;
for(var some in used){
if(used[some] == number) {
it_used = 1;
break;
}
}
if(it_used != 1){
trace(number);
used.push(number);
}
it_used = null;

должно работать, но не проверял....