Thanks a lot. That worked already very good. I experimented a little
bit more with this approach to enhance the distances between different
text elements (of cause without actually knowing what i was really
doing).

This one seems to keep the separation between the paragraphs while
maintaining at the same time similar distances as the DVI/PDF version
between the different text elements.
--------------------------------------------------
\Configure{paragraph}
{}{}
{\ShowPar\IgnoreIndent\HCode{<span class="paragraphHead">}\begingroup\bf}
{\endgroup\HCode{</span>}\par\IgnorePar}

\Configure{HtmlPar}
{\EndP\Tg<p>}{\Tg<p>}
{\Tg</p>}{\Tg</p>}
--------------------------------------------------

The following code gives correctly three paragraphs when compiled with latex and pdflatex:

-----------------------------------------------
\documentclass{scrreprt}

\begin{document}

\paragraph{Info Window} First paragraph.

Second paragraph.

Third paragraph.

\end{document}
-----------------------------------------------

But when compiled with "htlatex test.tex" only two paragraphs are generated. Here is the relevant part of the generated html file:

-----------------------------------------------
<!--l. 5--><p class="noindent" ><span class="paragraphHead"><a
id="x1-1000"></a><span
class="cmbx-10x-x-109">Info Window</span></span> First paragraph.
Second paragraph.
<!--l. 9--><p class="indent" > Third paragraph.
-----------------------------------------------

I.e. the first paragraph contains "First paragraph. Second paragraph.". If the class is changed to article, report, or book the result is correct.

I am using texlive-tex4ht-2011-13.5.1 under texlive-2011-13.5.1
on an openSUSE 12.2 system. tex4h.sty prints "version 2008-10-27-17:23".