bitcoind getblockhash 291050
bitcoind getblock 00000000000000004642ed8eb619f2f84aaf201dbf0ba5fc87c425d040455d5a
Whoa!! Thanks!!
The only problem with this is that bitcoind is not in the standard Mac download.
Bitcoin-Qt should operate in server mode if you set up the bitcoin.conf correctly. Then you can issue the getblockhash and getblock commands to Bitcoin-Qt instead of bitcoind