Yesterday, motivated by a friendly client, I finally managed to export the English (EN) and German (DE) versions of the arc42 software architecture template directly from their confluence spaces (at confluence.arc42.org).
In case you're using the Atlassian Confluence Wiki in version 4.2.x, you may grap the zipped xml files from the arc42.org download section.
Experience reports are highly welcome :-)
Update Nov 25th 2012: The current arc42.org template has been exported with our production version (4.2.x). In 2013 we accidently have no capacity to upgrade our confluence instance to 4.3.x. We apologize - but we therefore cannot provide a template export for the confluence 4.3.x branch. Hopefully this issue will be solved in early 2013.