http://www.answers.com/tribunal&r=67
"tri·bu·nal (trī-byū'nəl, trĭ-) pronunciation n.
1. Law.
1. A seat or court of justice.
2. The bench on which a judge or other presiding officer sits in court.
2. A committee or board appointed to adjudicate in a particular matter.
3. Something that has the power to determine or judge: the tribunal of public opinion."
But you are right they were called tribunals at Nuremberg. They were public though and there were specific charges and legal representation.
But you do make a good point about the war being over.
Generally speaking, at least in this context, a tribunal is a military court. You see, the basic charge against these people are violations of the law of land warfare.
Traditionally, such violations have been held to be beyond the reach of civilian courts since they lack both jurisdiction and the expertise to try such cases. Those brought before military tribunals do have most legal protections such as legal representation and due process. The rules of evidence can be different. For example, Miranda warnings are not required.
The Nuremburg tribunals were civilianized since the violations were not against the law of land warfare (generally speaking) but were considered to be crimes against humanity.
BTW, a trial is process, ie, being tried for a certain crime. A tribunal is a form of a court, ie, a forum for holding a trial.