I did one at IBM. there were about 5 of us sat in a room and we had to go through lots of bits of paper and decide who was the most suitable person to be employed as the manager of an eastern european company.
One bit of paper had, for example, that they didn't like women, another one had that they had to speak ubekistanish or whatever, another had that they needed a qualification... and we had to work through and decide together. It requires a certain amount of cooperation - they just want to see how you act with others.
Of course, I was pulling off my listening and being helpful act, and they were looking for people with leadership potential
If you have a rough idea of what they might be looking for, then it wouldn't hurt to try and show that you can do that, but being relaxed and just working together is a good idea. Listen to everyone, give suggestions as to what to do if no one else is forthcoming ... etc
' gratz on the MRes though