Why does the disk spanning function of PKZIP (command line version) not work under NT?

A. Because NT command processor CMD.EXE uses '&' character for separating several commands on the same command line and PKZIP uses the same character for creating multi-disk archives. Solution is to enclose '&' in quotes like this:
C:>pkzip "-&" -pr .

The other way of getting this to work is to precede the ampersand by a carat (above the number 6 on UK keyboard), as in -ex^&.

There is now a Win32 console (line command) PKZip 2.5 with disk span support. Check http://www.pkware.com

For more information see Knowledge Base article Q130893 (http://support.microsoft.com/support/kb/articles/Q130/8/93.asp)