Well, it wasn't that simple. But almost.
It turns out I had two problems. One was that BirdieSync was trying to sync calendars from both Outlook and Sunbird. It didn't like that. By trial and error, I discovered how to unselect the Outlook calendar. But Active Sync still wasn't happy. At one point it demanded my Microsoft Office 2003 registration code. Since the PC in question had only a 60-day trial version of Office 2003 installed, this seemed like a ridiculous request. But the only way to make it go away that I could find was to remove the Office 2003 trial version from the PC using add/remove programs.
After that, synchronization proceeded! BirdieSync delivered calendar sync between Sunbird and Windows Mobile Calendar and earns a SwampDrain rating of +2. I can now update my calendar on Windows Mobile, and have selected events published to my wife River's Apple iCal calendar, or other calendars that I may deem appropriate.
Given the performance complaints I'm reading about Outlook 2007, I am extremely happy I didn't have to swallow that blue pill after all.
Somewhere in this calendar interoperability saga is something profound. Perhaps I can coin Mace's First Law of Calendar Interoperability: Never use more calendar, or more interoperability, than you absolutely need.
The second law probably would have something to say about how no truly liberating interoperability solution exists unless some crucial component of it is open source, but I'm not willing to codify that just yet.
Device-to-device over-the-air calendar sharing is now my only vista (no pun intended) remaining for this blog. At some point I'll be replacing my ancient Dell Axim with a Windows Mobile phone -- or perhaps an iPhone, I don't know -- and will give everything a fresh look at that time. For now, the journey's had its rewards, at long last!