Well, after much consternation, I've got the WD seeing my WHS shared folders again (without repeating the windows installation process).
Thanks for the suggestions, willise, but unfortunately, I'd already been down those roads. I discounted all of those for the simple reason that everything was working with a virgin WHS installation, but stopped after a re-install.
In the interests of helping others with the same afflction, here's what worked for me;
1. Unplugged the network cable from the WD, reset to factory defaults and confirmed the IP addr was 0.0.0.0
2. Powered-down ALL network attached devices in the house; that's a lengthy list for me: 3 desktops, 2 laptops, 1 laser printer, 4 squeezeboxes (incl. Controller), 1 iPod, 1 PS3, 1 VOIP adaptor and 1 WDTV-Live.
3. Powered-down the main WRT54GL router and the BEFSR41 router (switch).
4. Power-cycled the cable modem and began poweing-up devices in reverse order; WRT54GL, then BEFSR41, then WDTV-live (network re-attached) and then the WHS desktop/server. Remaining devices to follow.
After confirming that the WHS server and WDTV-live had valid IP addresses, I checked for Network Shares on the WDTV-live and Voila!, it was seeing the server again and I could troll and play various video content.
None of this changes my opinion that in its current form, the WDTV-live is a fragile, temperamental, bug-riddled product prematurely rushed to market.
But for now, I'm happy again...