Ok, it's actually rather simple.
When you click the box to convert from windows to mac paths, it removes the drive letter *and* changes the backslashes to forward slashes. So it's ignoring your find and replace rule, because it doesn't match.
All you want to do is put /Volumes/video in front of the existing file paths right? For example, the first one in the screen shot should be:
/Volumes/video/Documentaries/Shiela Hancock Brushes...
To do that, just turn on the directories part of the tool, up above:
Directories: (checked)
Base Path: /Volumes/video
Rule: (blank)
Keep the find and replace turned on, so it will do the conversion from windows to mac.
Also, VERY IMPORTANT, make sure to change the mode at the top. It's set to RENAME right now. You want it set to UPDATE database.
You should try this on one or two files first. Once that works, try it on a group of files. Then do more, or all of them.
Good luck, and let us know how you do!
Brian.