Guy,
Thanks so much for your quick reply!
Lua is an interpretive language with an interpreter that's somewhat 
compact and embeddable.  Wireshark can be built with Lua support - the 
Windows version we distribute is, I think, and other binary versions 
(various Linux and BSD packages, etc.) might be built with it either.
Hmm, the version I had with my distro (Debian Etch) was 0.99.4 but still didn't have Lua built in.  So I downloaded the latest version from the website, 0.99.6, and configured it with Lua support.  Here's the command I used:
piers@akane:~/src/wireshark-0.99.6$ ./configure --with-lua=/usr/include/lua5.1/
Then the final result was:
The Wireshark package has been configured with the following options.
                   Build wireshark : yes
                      Build tshark : yes
                    Build capinfos : yes
                     Build editcap : yes
                     Build dumpcap : yes
                    Build mergecap : yes
                   Build text2pcap : yes
                     Build idl2wrs : yes
                     Build randpkt : yes
                      Build dftest : yes
                    Install setuid : no
                       Use plugins : yes
                  Build lua plugin : yes
                  Build rtp_player : no
               Use GTK+ v2 library : yes
                       Use threads : no
            Build profile binaries : no
                  Use pcap library : yes
                  Use zlib library : yes
                  Use pcre library : no
              Use kerberos library : no
              Use GNU ADNS library : no
            Use GNU crypto library : no
            Use SSL crypto library : no
          Use IPv6 name resolution : yes
              Use Net-SNMP library : no
                Use gnutls library : no
But when I started off the compile, and it got to the Lua module, it exited fatally with the error snippet:
In file included from ./wslua_tvb.c:31:
./wslua.h:40:17: error: lua.h: No such file or directory
./wslua.h:41:20: error: lualib.h: No such file or directory
./wslua.h:42:21: error: lauxlib.h: No such file or directory
What am I doing wrong and how do I fix this please?
Thanks very much for your time in advance!
Regards - Piers