Call template file, hook_theme() thru theme( hook, $data )
Your code looks fine to me; make sure you've cleared Drupal's caches since implementing hook_theme(), and your preprocess function, as these implementations are cached, and won't show up in the registry until you do.

FYI, the "path" property is not required if the template file resides in your module's folder: Drupal will check there first anyway (this won't be causing the problem though).