Good news, everyone. Thanks to Tomek from libgadu and pidgin, I was finally able to build Kadu 1.0-rc2 for Windows. It lacks several plugins (all external ones, spellchecker and otr), but it works almost flawlessly.
You can find packages at my project at OpenSUSE Build Service. It is RPM that can be unpacked with 7zip It contains only one file - Windows installer. I will put installer on Kadu download pages when I resolve problems with spellchecker and otr plugins. Then I will start work on external plugins (probably some small maintenance will be needed).