Try: understand the xml-export available under special page. Export at least two pages you created.
First follow the advice to use Open Office mediawiki export to preserve as much formatting as possible.
This: http://biowikifarm.net/meta/Converting_Word_to_Mediawiki_text many help or not.
then prepare your Wordprocessor file: replace & to & > to > and < to <
Now replace the "article" borders with the stuff you find between the pages in your xml export.
The catch is to give each page the right title. If your base structure is well defined, and you know end or previous to next title, end of title to start of page content, you should be able to do it.
Add the start and end of the export "xml"
Save as plain text. Use an xml validator to check you did it right. This is crucial...
Then try to import a small subset first.
This may help - or not: http://biowikifarm.net/meta/Mediawiki_XML_page_importing
good luck!
Gregor