I found Stefan Seidel's Answer for: Disable internet access but leave LAN working at: Disable internet access but leave LAN working
I found that the command line entry to disable internet access was required again after each re-boot, which is fine by me.
However, what I was originally trying to do, and ensure, was to prevent external (to my router) internet access to this particular XP machine AND maintain internal (LAN) connectivity between it and other PCs on my home LAN getting their IPs from said router, which is an old Linksys WRT54G V8.
I thought it would be best to ask Stefan to clarify whether his solution would be an effective inbound internet IP blocker, however, as a newly registered superuser.com user, I don't see a method of contacting him directly.
Thanks, Kevin