Installed latest Bitcoin-Qt, fully synced, but 'getreceivedbyaddress' etc doesn't work?
getreceivedbyaddress only works for your addresses, i.e. those for which the private key is in your wallet.  Those are the only addresses for which bitcoin-qt keeps indexed transaction data.  Getting balance and transaction information for arbitrary addresses is unfortunately not supported by bitcoin-qt; sites like blockchain.info write custom software that manually parses the block chain.

See also this answer.