"An NNTP client would actually be a SERVER to a desktop PC. It COULD be your PC, but it's unlikely unless you're specifically enabling the NNTP protocol which virtually nobody does (and would not be smart unless you know what you're doing)."
FYI: Anyone can see for themselves if you have an active NNTP client on your machine.
Go to http://www.grc.com/x/ne.dll?bh0bkyd2
and do a "Common Ports" probe.
If it shows NNTP (port 119) as "Stealth" you do NOT have an NNTP client running on your machine and your firewall is blocking the port.
If it shows "Open" (or whatever) you MAY have an NNTP service running IF most of your others ports are shown as "Stealth". You do have a security vulerability, though. I doubt if ANYONE has this situation.
If all of your ports (or most) are open, you don't even have a firewall and your computer is at significant risk.