Media Mover and thumbnails
I can only assume your media mover process is upload file(s) to site, moved files to S3, copy S3 file location to the CCK field

For Drupal 6:

Install imagecache module and its dependencies.   Create a imagecache preset call thumbnail of the size you want.

Create a view.   Add the CCK field.   In the settings select the format of the thumbnail preset.