Am I right in expecting that the address should have 0.002 coins in it?
Yes.
Quote
Where can I find more information about how to spend these coins and when/how they will be spendable; or if I am wrong about this, an explanation to fill in my knowledge gap?
As Pieter said, they don't count towards your wallet balance because you don't have ALL of the private keys in your wallet.It is not clear which wallet those 1-of-2 coins belong to, since neither has exclusive control over them. So the code is conservative and doesn't add them to your balance unless you have ALL of the private keys.
Quote
Is there an estimate for when multisig will be usable? Is it already usable? If it's already usable, can someone point me to the info I require to be able to use it?
The 0.7 release will have a set of RPC calls to create and sign transactions that spend from multisig inputs: see https://gist.github.com/2839617