Can I send message inside the transactions script? I would like to send transactions with messages as described in the wiki. In Transaction with slightly changed script is never relayed, someone answered that non-standard transactions are not relaid by the client. I was wondering if this will affect this type of transactions.

Also, I would like to know if there is a source code that implement this functionality. I need to send small data (SHA256) as a digital signature that can be view by all the peers in the network and is associated to this specific transaction.

Thank you very much and your help is very appreciated
You will find that non-standard transactions are very hard to get into the block chain. Instead, encode the additional information as accounts and send a single satoshi to each account needed to convey your message. That way, you can use standard transactions.

Transaction 28ccf29cfcc9f82d42793db770e7c7894d61ccf3d18299f34bda2e54415da287 is a particularly silly example of this.