As I take it, it's not really possible yet. In any case, we're talking about 'multi-signature transactions' [0]:
A multi-signature transaction is one where a certain number of Bitcoins are "encumbered" with more than one recipient address. The subsequent transaction that spends these coins will require each party involved (or some subset, depending on the script), to see the proposed transaction and sign it with their private key. This necessarily requires collaboration between all parties -- to propose a distribution of encumbered funds, collect signatures from all necessary participants, and then broadcast the completed transaction. [0]
If you are using Blockchain's Mywallet, you might already be able to use them, as an end-user. [1]
One way to implement them is by allowing a more generic 'script execution per transaction' (not sure of wording) mechanism, proposed in BIPs 16 and 17. [2] [3]
Also see bitcoin.stackexchange question about multisig TXes. [4]
As I understand it, if you're a developer wanting to implement arbitrated bitcoin transactions, you'll have to wait. Correct me if I'm wrong though.
One way to implement them is by allowing a more generic 'script execution per transaction' (not sure of wording) mechanism, proposed in BIPs 16 and 17. [2] [3]
Also see bitcoin.stackexchange question about multisig TXes. [4]
As I understand it, if you're a developer wanting to implement arbitrated bitcoin transactions, you'll have to wait. Correct me if I'm wrong though.
[0] https://en.bitcoin.it/wiki/BIP_0010
[1] https://blockchain.info/wallet/escrow
[2] https://en.bitcoin.it/wiki/BIP_0016
[3] https://en.bitcoin.it/wiki/BIP_0017
[4] http://bitcoin.stackexchange.com/questions/3718/what-are-mul...