Not necessarily. The key is used to sign the coins, and right now it's generated by the program. The REST of the program, however, doesn't care where that key comes from.
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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