Well, thanks to the help of all here my problem with zlib is finally solved... so I get to see entirely new exceptions when I launch TreeLine, yay :-)
First, I found that the "locale" subsystem on the Z (Cacko 1.21) does not seem to like the standard python idiom :
(dies with: "locale.Error: unsupported locale setting")
The only syntax I could get to run was locale.setlocale(locale.LC_ALL) (no locale parameter). This required changes to the app's code but also in locale.py.
After that the app finally got around to importing some stuff from the qt package... and stopped right there on the first line, with :
ImportError: unable to import name QColorDialog
(and also QInputDialog, and probably others)
What I'm wondering here is whether this is just a naming issue (like the QApplication vs QPEApplication thing) or a deeper mismatch between the versions of Qt/PyQT used by the app's author and those available on the Z. His app works with the old freeware version of Qt for Windows though, so it's not *that* sensitive...
In other words : is it hopeless to want to port an existing, non-trivial PyQt app to the Zaurus, and is the Z's (Py)Qt only useful for developing from scratch on itself ?