Originally Posted by HarryT
You really DO need to have a basic knowledge of HTML, Mike. This is simply a part of the writer's "toolkit" and there's no getting around it. It's as basic a requirement as a carpenter needing to know how to use a saw. Both the popular eBook formats (ePub and Mobipocket) are HTML-based, and being able to "tweak" the HTML that the tools generate for you is vital.
Harry is right that some knowledge of HMTL is a useful skill in getting your work presented just so. However, there are various tools available to convert formats, and lots of people (in this forum, for example!) who can help if you get stuck with something in particular.
By far the hardest part is writing the novel in the first place
You won't do any harm by writing your novel in Open Office, and converting it when the time comes into the various target formats that you might choose. Nobody writes in ePub from the get go - never mind in HTML.
My advice would be to write the novel, do a basic conversion to the target format in Calibre, then ask for help on any specific queries to get it to look how you'd like.