I've done a new tutorial that explains how to use KDevelop and Designer together to develop KDE applications visually. See it here
The package includes a directory with some html files which explain every single line of code written for this tutorial. It also includes the automake/autoconf scripts to generate the makefile and everything needed to build the tutorial.
Alternatively, some of these pages are also online, and you can browse them from this link. Please note that you cannot build the tutorial just by copying the code from those pages, it's better to use the above package.
The spanish documents are browsable at this link online.
For those of you preferring to read spanish , you can download a spanish version of the explanations (translated by my brother, Rafael, and me) from the following link : kdetutorial-es-1.2.tar.bz2 (24 Kb.) . This version only includes the documents, so you'll need the full version (above) to compile the example applications.
NEW: The tutorial has been translated to romanian by Bogdan Daniel Vatra and Claudiu Costin. You can read it from this link online or download the whole package (recommended) from kdetutorial-1.2-ro.tar.gz . Thanks for your translations!