Although it wasn't a full blown trial, I ran something similar like so:
The Sitch: A knight (a member of the player's house) is accused of poisoning his opponent before a joust, and thus the reason for his victory.
The PC (as heir to the House) acted as the defense, and another group of NPCs (the house of the poisoned knight) as the "prosecutor", and then the Lord Paramount as the judge.
Each side had their own objective: for the PC - prove his household knight didn't do it; for the NPC accusers - prove he did; for the Lord Paramount - find the truth. In the case of the two houses, they needed to defeat the Lord Paramount, but in his case he needed to defeat either of them. I did however, allow other outs, and they were partially used - either accuser or defender could direct their influence at the other party in an attempt to get them to break (in this case, the accuser tried to provoke the defender into attacking, to show his temper and get the Lord Paramount to rule in favor of the accusers).
To add to the complexity (and fun), the Lord Paramount's heir was present, aiding and mollifying his father, the accused household knight was there to support the PC heir in his defense, and the liege lord of the poisoned knight was there to support his bannerman.
Interestingly, it was in a PbP game, so you can read about the details starting here: http://www.myth-weavers.com/showthread. ... ost5608005