(from http://wiki.xbmc.org/index.php?title=Video_library/Home_videos/custom_videos)

To add a video such as a home movie or other video that are not normally found by XBMC’s scrapers, try using an NFO file.

Create this file and save it in the video directory.

Here’s a basic/bare minimal example of an NFO file:

<?xml version="1.0" encoding="utf-8"?>
<movie>
<title>Some title</title>
<originaltitle>Some title just in case - you most likely dont need this either</originaltitle>
<sorttitle>It will sort by this title if you include it</sorttitle>
<genre>HomeMovies</genre>
<id>-1</id>
</movie>

XBMC will only look at your NFO files ONCE. To refresh a lot of videos with custom NFO files (say, when you’ve updated the NFO file itself): Go into Files, and on the source you added for your custom videos – Set content and pick <None>, then click OK. Then set content again as if you were adding them for the first time.