OpenOffice to MediaWiki
Mediawiki export is built into OO from OO 2.4 onwards. Simple choose File > Export, and select Mediawiki from the dropdown list of formats.
If you are on OO below 2.4, you can use these plugins to produce mediawiki documents:
You can also install OO 2.4.1 via portable apps: http://portableapps.com/apps/office/openoffice_portable
Note: OO will export the files with ".txt" extension. In case you're on mac, you might double click the file, and it opens in TextEdit. TextEdit doesn't understand the utf characters, and so special characters are garbled. Use another editor (such as emacs, or OO!) to open the text file, before pasting it across to mediawiki, and all is well. Of course you may want to replace some of the utf characters by ascii equivalents.