Ooops! Yes! You're quite right if the PGP key is compatible with the key type used in BitCoin. I still associate PGP with RSA and I believe BitCoin uses ECC so I was thinking you'd have to update the software to understand RSA keys.
A production version of BitCoin will probably have to accept a number of different Public Key algorithms.
ByteCoin
Right, I thought we were talking about a private key that was the same type as the client (and assuming the client uses some known standard). Obviously it wouldn't work if you were to provide an unrecognized type. =P
However, changing the client to recognize multiple types of PKA's WOULD most likely be a breaking change, unless satoshi is including some kind of version information about what keys were used in the block chain.