Firewalls protect sensitive internal records from Internet client software snooping. Anyone working for these companies would see very little difference in the way they would use an intraNET or the Internet. As you might suspect, NCs run on intranets with ease. A fat client is a software program loaded with functionality. Microsoft's Word 6 would be an example of a fat intranet client.
Fat client can do almost anything but toast corn muffins.
In contrast, a thin client might be something like a small word processor that is only 400k bytes in size - no spell or grammar checking, and a more limited number of fonts. NCs would use thin clients. Frankly, I like chubby clients. A final thought. The success of the NC is not assured.