Thanks, everyone, for the replies.
I'm very much sold on the 29"er aspect of this project. I have been riding a 29" hardtail since fall of '02 and am sold on the workings of the larger wheels. I'll jump to a 29" solo full suspension when the right bike comes along. As it is, my thinking is that for a non-suspended tandem, the 29" wheels will provide a significant advantage in rolling smoothness (sort of "built in" suspension if you will) and if I'm forced to hit the trails on a rigid bike in the solo configuration, I'd have it no other way.
On one hand, I am slightly concerned about going "all out" with a custom build out of the gate. On the other hand, my wife and I have rented ill-equipped tandems on a few occassions and done some decent riding on them, including some choppy trails in the Marin Headlands, and we both agree this is something we want to persue. Specing a rigid fork and rebuilding the Speedhub of my 29"er into a tandem-worthy wheel will make a significant dent in initial costs.
TG, I signed up for your Yahoo! group and will check out the thread as soon as you approve my request for membership.