Importing wiki pages
There is a script in the attachment:wiki:TracWiki:mediawiki2trac.py WikiProcessor for the MediaWiki has been started as trac plugin on http://trac-hacks.org/wiki/MediaWikiPluginMacro.
It is also possible to convert MediaWiki to MoinMoin for example and use scripts below.
See the script by kgk at TracHacks - http://trac-hacks.org/wiki/MoinToTracScript MoinMoin wiki pages include converters for other wiki flavours - http://moinmoin.wikiwikiweb.de/ConverterMarket
TWiki archive can be converted to MoinMoin archive using the script provided with MoinMoin to TracWiki converter at TracHacks.
There are some universal converters which could migrate pages back and forth over several formats and got converted to Trac using some of the recipes above. Here are: Universal Wiki Converter and WikiAPI applications.