How can I copy an address (with the private key) using JSON-RPC? I need to be able to create an address in 2 different Bitcoin-qt instances (actually 2 different PCs).

I can create it using "getnewaddress" on the first one but how can I import it to the second one with the private key?

Thank you!
Check this section out: https://en.bitcoin.it/wiki/How_to_import_private_keys#Using_bitcoind

Essentially you can use importprivkey

$ bitcoind help
[...]
  importprivkey &lt;bitcoinprivkey&gt; [label]