I have the 0.5.3 version, and I was reading up the old manual here
http://code.google.com/p/sigil/wiki/BasicTutorial which shows a TOC editor. I was trying to recompile an epub which had some missing chapter headings, but I cant for the life of me, find the TOC editor, as mentioned in the old manual. I have read the updated Manual, but it has no info on how to give a title to the chapters in the TOC headings.