For the DV 2011 the USA State Department had announced the list of countries which are eligible for the DV Lottery 2011. Here is the list of countries whose natives can't participate in the DV lottery 2011 program according to the DV 2011 instructions. This is because that these countries did send more than 50,000 people within the past 5 year’s period.
BRAZIL,
CANADA,
CHINA (mainland-born),
COLOMBIA, DOMINICAN REPUBLIC,
ECUADOR,
EL SALVADOR,
GUATEMALA,
HAITI,
INDIA,
JAMAICA,
MEXICO,
PAKISTAN,
PHILIPPINES,
PERU,
POLAND,
SOUTH KOREA,
UNITED KINGDOM (except Northern Ireland) and its dependent territories, and VIETNAM.

Persons born in Hong Kong SAR, Macau SAR, and Taiwan are eligible.
If you were born in an eligible country here are some other ways to be eligible for the draw if you meet the requirements.

Read the DV 2011 instructions.
http://www.travel.state.gov/pdf/DV-2011instructions.pdf