It doesn't really matter whether you add blank lines or not. The main thing to give yourself an easy life when using Word to create HTML (filtered) to import to calibre is that you use the Word built-in styles 'Heading 1', and/or 'Heading 2', and/or ... 'Heading 6' to style your chapter headings.
The created HTML will then contain <h1> and/or <h2> ... <h6> tags around your Chapter headings.
It is then very straightforward to tell calibre to use these heading tags to detect new chapters and to make sure each chapter starts on a new page.
If you need more details feel free to ask.
Last edited by jackie_w; 12-21-2010 at 12:18 PM.