See this comment from Gavin :
https://bitcointalk.org/index.php?topic=82213.msg906833#msg906833Edit : Basically (if I get it right), you can make a multisign Bitcoin address using the command line (but no user-friendly GUI). And to spend funds sent to this address, many seperate people have to sign the transaction. So this is not as simple as sending a transaction from your computer. Some work still need to be done on this part.
Thanks!
Specifically, if you want to release the entire amount and you do trust one of the individuals to hold the funds short term during the signing process, you can just combine the private keys into one instance of bitcoin-qt and then spend the funds.
If anyone can document a better, more distributed way to combine signatures on specific transactions that spend from the multisig address, please do so.