I use Videora to convert videos and DVDs to IPod format - it automatically adds them to ITunes.
If it's not showing up, use the search box in the top-right to search for it. Sometimes files show up in odd places and that will find them. Failing that, it could be that the file is corrupt or not in the right format. If that happens, ITunes will silently (and unhelpfully) fail to add the file and won't tell you why.