Protecting Video from other uses

I did a search and couldn't find exactly what I was looking for so I'm hoping you guru's can help (as I'm a bit of a beginner in this area). Anyway, a client had one of their training videos (originally encoded in Windows Media 9)posted on YouTube. Of course this had proprietary info, etc., and they are investigating the issue (maybe someone's getting fired!). However, they wanted to know what they can do to help prevent easy "Save as" from their media players and make it more difficult to steal.

Their typical workflow is to provide a link (through email) to a video file on a folder.

While I told them that any video can be "grabbed" or saved (almost as easily as someone grabbing an important memo, etc,), it is just a matter of making it more difficult for the user to do so.

I initially mentioned Flash - their IT department agrees, and they may consider streaming only to the desktop, but what other options, pitfalls, or advice might I be able to pass on?
Thanks so much!