Are the words "network packet" and "network package" interchangeable?

Packet and package are certainly different in IT terms.

A packet is a small piece of data, that needs to be combined with other packets to create a whole. This is how data is transmitted over a network, by breaking it into packets of a few bytes: http://www.computeruser.com/dictionary/packet/

A package refers to an entire piece of software, that can be installed and operated by a user: http://www.computeruser.com/dictionary/software-package/

A software package would be broken into packets to be sent over a network, and the packets would then be reassembled into a package at the destination.

Network package is technically incorrect, although the meaning can be easily inferred.