I also have an URL with this secret code. All we need is to decrypt it somehow to the private key. I guess this is possible, but unfortunately there is no contact with the instawallet owner. See also this thread:
https://bitcointalk.org/index.php?topic=5305131.0DM me if any updates. Block explorer shows that my very very old satoshis are still in my instawallet address, now worth a couple of hundreds $.