Ant has a support article on how to direct NEW videos to a different folder, but it says you have to move the old videos yourself.

http://support.ant.com/entries/20354643-How-to-change-the-directory-of-downloaded-videos-

Note: On the Add-ons page, you probably need to change the category to Extensions in the left column to make that settings change.

Does it work?

Sorry to respond so late. I tried it but after clicking Add-ons, couldn't tell if I was clicking the correct Ant Video Downloader and the one that I did didn't have a preference icon, save the one on the toolbar that I tried to used before with no success. So I clicked the preferences on the ant.com tool bar but couldn't see how to change the directory. I'm copying the ant video folder to the new HDD but suspect that it won't work.

Sorry.

How many Ant video downloaders do you see? I do not use this add-on, so I don't have any experience with what you should be seeing.

On Windows, the button is called Options, and on Mac, it should say Preferences. If you see Options for the extension, try that. You also could try the "More" link.