Do you want to create a NovaMind 4 or NovaMind 5 file?
I would highly recommend creating a NovaMind 5 file as we have made the file format a lot simpler and the application is a lot more forgiving when opening files. (most elements are optional)
Quote from our plugin page
Easy file format
A .nm5 file is a ZIP compressed archive containing separate XML documents for content and styles and contains images and attachments.
We tried to keep the file format as simple and intuitive as possible and most elements are optional which makes creating .nm5 files easy. If you want to parse .nm5 files you will see that the structure is simple and consistent.
There is no public file format specification available yet but it is really easy to create a document.
To get started you create a content.xml file that will look similar to this one:
<?xml version="1.0" encoding="utf-8"?>
<topic-node id="66443e0f-ea12-4cb7-b9cb-3b666a97f015" topic-ref="ef79b32a-2479-422b-8830-f2c64527ac7b">
You then zip it and change the extension to .nm5.
Should be pretty self-explanatory. One important thing you should be aware of is that the id's should be unique and a topic-node needs to refer to a topic via the topic-ref attribute. The rich-text element should also specify the xml:space="preserve" attribute.
Images are a little more complex as you also will have to create a manifest.xml file. I suggest you create a mind map in NovaMind 5 that looks like the one you want to create and then look at the resulting files. (document.xml and manifest.xml). You can ignore the style-sheet.xml and the theme-ref on the maps. Also most of the 'styles' can be left out.
Hope this helps you to get started.