OK, so it took a bit longer than a week, but I went through nl.po by hand now. Removed some linebreaks (both in English and in Dutch bits), made a few more changes and doublechecked encoding.
I'm aware of the 'map' vs 'directory' discussion, but wasn't aware 'directory' is in the so called 'groene boekje'.
I have the following now: where the English bit says 'dir' or 'directory' it says the same in Dutch. Where it says 'folder' in English, it says 'map' in Dutch.
I'm building the 20071015 tarball now with my latest nl.po, to check if my linebreak-removal didn't break something else. If nothing funny turns up I'll upload my nl.po tomorrow.
edit:
I merged my file with the latest amule.pot (couldn't find source_string.po). That has some weird line-breaks too, probably something to do with line length. Anyway I took that as a guide for one last check, translated some extra bits and switched the file to utf-8 (it was still in ISO-8859-1). My builds look OK, but a strange symbol might have been left behind somewhere as a result of the switch (I doubt it though).
The result is attached