As you suspected, the Terminal Services process was indeed not running on my XP system.. So once I started the process, OA's network activity graphs began functioning normally. You sure figured that out quickly!
I hate to admit it, but I actually had intentionally disabled the Terminal Service process, because I wasn't using "remote desktop" or "fast user switching"; and knew that the Terminal Service process was a favorite target for hackers looking to compromise a system. So it seemed prudent to disable it. I had no idea that OA depended on the Terminal Service process for its network activity display!
I'm sure there are good reasons for that design decision; but from this ignorant user's perspective, it seem ironic that a security product like Online Armor would require users to activate a powerful, vulnerable process like the Terminal Service, simply to display status data.
Anyway, now that I know the problem, I need to decide if having a functional OA network traffic graph is worth the risk of continuously running the Terminal Service process that I don't otherwise need. Now, if I were an ideal 'me', I would manually start the Terminal Service process each and every time I needed to monitor network traffic via OA; and then halt the process when I was finished. More likely though, I'll just throw caution to the wind, and leave the process running all the time. Yes, I am quite the wildman. ;-)
Thanks again for your help!