From the DV-2011 Instructions:
Q: WHAT ARE THE REQUIREMENTS FOR EDUCATION OR WORK EXPERIENCE?
A: The law and regulations require that every entrant must have at least a high school education or its equivalent or have, within the past five years, two years of work experience in an occupation requiring at least two years’ training or experience. A ―high school education or equivalent‖ is defined as successful completion of a twelve-year course of elementary and secondary education in the United States or successful completion in another country of a formal course of elementary and secondary education comparable to a high school education in the United States. Only formal courses of study meet this requirement; correspondence programs or equivalency certificates (such as the G.E.D.) are not acceptable. Documentary proof of education or work experience must be presented to the consular officer at the time of the visa interview.
High school education is the minimum education required. Actually, when you fill in the DV form, they ask you what is your highest education (not the minimum). My understanding is that you don't need the HS diploma but anything could happen when you go to the interview.
Good luck