[Koha] new to koha: where to get z39.50 servers?

Hello, I maintain a little bunch of computers in a local community center. They wanted to make a catalog of all the media and books that they have in their little library (a few thousand books). I am learning about library management stuff as I go along ... and only as much as I need to know for installing Koha. I have installed Koha on Ubuntu Feisty (soon to be upgraded to Gutsy). I am wondering, how do I add Z39.50 servers? Do I need any kind of authorization to connect to various such servers (username and password)? Are there any open ones? thanks for all the help, ->HS