As Danny said, getrawtransaction and decoderawtransaction is the easiest way to go.
If you checking transactions not related to your wallet, you need to enable the transaction index. Bitcoin uses another method since some version (forget which), due to the tx index being more resource intensive.
To do this, just add:
txindex=1
to your config, shut down bitcoin-qt or bitcoind (if already up), and run
bitcoind -reindex
This will take some time, as it has to go through all 10GB of data to make the tx index. In a production environment this can be seen as unacceptable, but easy enough to get around.