If you are using the dvd to produce an assessable income, then it would likely be deductible. Depending on the cost, you may need to write it off over a number of years. If you have no rental properties currently, or only one rental property and the dvd set is on doing property renovations, then it is unlikely it will be deductible.
May I also suggest a book on spelling and grammar, not tax deductible, but will help you tremendously.