I would suggest that you consider making streaming videos that are promotional in nature at the relatively low resolution appropriate for streaming. For instance, if you have a tip or technique that is now widely accepted in the sailing community (the buckets with the flap bottoms to reduce rolling comes to mind), you could digitize that "tip" in order to promote the DVD you wish to sell. Think of it as an incentive to learn more.
I would also suggest you stream them on YouTube.com rather than on your own site, because then you aren't paying for the bandwidth. A simple overlay of the website name on the "sample" video, or a card saying "for more, see our website" at the end of the "tip clip" might generate more hits for you and consequently more sales of the DVDs/books, which I presume is your goal.
Large corporations are frequently up in arms about music piracy and unauthorized videos, etc., but from personal experience I can say that the vast majority of my book, music and video purchases over the last five years have come from hearing a download, seeing a clip or reading an excerpt from a book I thought would meet my interests. In other words, the ostensible "giveaway" led directly to a purchase of an artist or writer I would otherwise have never heard of, or realized might be of interest to me.
This is why I can see that, particularly for the low-volume, special-interest content creator (in your case books and videos), what may seem like a freebie is actually just another marketing tool, and one with the potential to be particularly effective.