Help:How to import private keys in Bitcoin Core 0.7+
1st you must unlock your wallet:
Then go to menu: /Help/Debug Window
Now click on the tab - Console.
In the console at the very bottom is a text entry box in here enter: importprivkey yourPrivateKeyInWalletImportFormat TheLabelThatIWant
Note that this can take a good few seconds and during that time it looks like the client has hung!
Once Imported you can check that you have the address by closing the Debug window and going back to your address book. In there you should see the address you imported and the label.