Problem importing existing key?

Hello,
I have an old key that I had made in PGP Desktop a long time ago and want to know if I could re-use it? The only problem is that I just have the key exported in a .txt file (with begin, end PGP block) and nothing more. I am unable to see how I can import it into FireGPG so that I can also enter my password as a private key. I assume that the private key is nothing more than that pass phrase that I entered back in PGP Desktop when I created my key. Am I missing something?

Even if I create a new key through FireGPG key manager, and export that key, when I delete it from the manager and try to re-import, I can only get the public key version. So when I go to gmail and try to send a message to myself with that re-imported key, I am able select the public key from the list, but when it's time to select a private key there are none in the list.

I am running Windows and have a successful install of Gpg4win.