To get the private key of a specific address in Armory:
- Open Armory
- Double click on the wallet that contains the address you sent funds to
- Double click on the address that you sent funds to
- Click on "View Address Keys"
- Enter your password and click Unlock
You then copy the private key and import it and/or sweep it into the wallet program of your choice.
You can repeat the above process if you sent funds to more then one address.