BookCreator may be an option. I'm not sure how well it works when importing existing Word documents, but it is a Word to ebook tool and can output several (DRM-free) ebook formats. See also the link in the BookCreator thread to other conversion options (LIT in particular).
Otherwise, MobiPocket Creator will import directly from Word .DOC files (but you would probably need to learn how to use the TOC tool and other features) and Calibre can import RTF and produce an ePub (you may need to customize its chapter detection).
In the future, it may be possible to only create an ePub and import this to MobiPocket Creator (or the command line program mobigen). But at present this "ePub to MOBI" approach does not convert the ePub's TOC to MOBI.