I ended up using dpkg / apt to remove all the Deb software versions then compiled and installed qmail, tcpserver, vpopmail, qmailadmin etc, from source. With everything then in the default locations, and no Deb Woody stuff getting in the way,way, the problems just seemed to evaporate...
Probably the packages installed themselves into various Debian-specific locations and then conflicted with the install from source.
For important stuff, I find it generally better to always install from source and use the package systems just to manage the underlying OS.
-- Aj. Systems Administrator / Developer