Writing documentation for software

Hello,

I'm working on a desktop app using Gnome technologies and I'd like to
write documentation, both developer docs and a user manual.

So far, the only GUI tool I've been using for serious documents is LyX,
which produces LaTex files I convert to PDF.

But now I need to write software docs and Mallard seems to be the way to
do it. What are the tools for easy creation of Mallard/docbook
documents? Can I still use LyX? If not, are there WYSIWYM tools like
LyX, which produce Mallard files? Or I need to write the xml/sgml source
by hand?

Thanks in advance
Anatoly