We publish all of the available import specs at
http://www.infopop.com/yaml/The Invision one isn't there currently, as it's still in QA. With luck, I'll be able to get it past that phase today and published very soon. If you need it before then, please open up a support ticket, including the URL to this topic, and ask that the ticket be assigned to me. <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
Now, if you wish to MAKE an import spec file... that's another thing entirely. I would suggest by looking through all of the available ones. The format may well jump right out at you...
Do note that it's best to try importing with 6.5.1, as there are a couple known issues in the 6.5 importer that could prevent it from working as expected.