Both game and Noport were absolutely right: I missed a step. At the bottom of the server guide I missed the following line:
You will also need to copy the two DLL files that you downloaded earlier into your C:\Windows\System32\ directory if you do not have Everquest Titanium Installed.
The last time I set up a server I had Titanium installed so I didn't need to do it. This time I'm running Underfoot and forgot about the dlls completely. I copied them to System32 and guess what, everything worked perfectly. Funny what happens when you actually follow the directions.
Underfoot - still getting unknown opcode errors, but it connects and doesn't crash
Quests - working perfectly
Items - loading properly
LAN connections - working perfectly with Windows 7 64-bit
External connections - working perfectly (Hamachi Login is awesome)
I still have a handful of tweaks to make -- like why GM accounts get a Respawn window when they die -- but overall the server is UP AND RUNNING!
Thanks guys