Thanks for the suggestions, Mac, I finally got it working!
I re-installed last night and was able to play online without the 1.1 patch. It was tough to find a server, though, let me tell you

.
Next I installed the 1.1 patch and back to the same problem - no internet play. In a fit of desperation I finally opened up the UDP ports they specify in the manual and what do you know, it works.
I don't know what the heck they did in the 1.1 patch, but they somehow must have enforced certain port usage that they hadn't bothered with before. To what end I can only imagine.
Anyway, I guess it's all about opening the proper UDP ports on the firewall. *sigh*