Here's a brief khan-academy style video explaination:
https://www.youtube.com/watch?v=boPW1FwNu4c
It's a part of this tutorial:
https://github.com/orisi/wiki/wiki/Mastering-Distributed-Oracles
In short: you create a multisig address that locks the money in, and will be unlocked using one or more impartial arbiters/oracles.
The current Orisi examples assume that oracles are the only ones who sign the tx, but you could add sender/receiver's signatures to the mix to be sure that oracles won't run away with money. (it's described within the whitepaper: https://github.com/orisi/wiki/wiki/Orisi-White-Paper )