To add a list of Newsletters into NetCommunity, you will have to add them manually.

There are no features to import lists of Newsletters; these must be created within the Newsletter section of NetCommunity. If you already have existing Newsletters that you are trying to add, you will have to re-create or copy them into the Newsletter section. Once the Newsletters are created, they automatically appear on the "User Preferences Email Form" for users to opt-in or opt-out.

For more information on newsletters, see the users guide:
http://www.blackbaud.com/files/support/guides/bbnc/emailre.pdf