Can somebody help me with step-by-step list of how to create a multi signature 2-of-3 transaction?
It seems some partial implementation exists. Quoting Gavin:
Generate a multisig address:
Spend from a multisig address:
This isn't implemented yet (RPC calls mechanism). You could gather up all addresses into one wallet, and then you would be able to spend the funds.
Update March 2014
Multisig is still hard. I believe the SX library is an easy tool (by people like Vitalik Buterin and Amir Taaki) for working with multisig, but I haven't tested that myself.
Actually, both receiving funds at and spending funds from a multi-sig address is already supported.
You can find the code to do so, plus comments, by Gavin: