ChadC,
I was in a similar situation to get all my music off my computer an onto an external drive. What I did is I first set my music folder to be the folder on my external HD that already has all of my music. Then what I did is go up to the "File" menu while in iTunes, and select "Add To Library". Then select the folder on your external drive, which will then create a new iTunes library based on what is in that folder.
What I don't know is how to export playlists.
Hope that helps