The Bureau of Labor Statistics is always a great place to look.
Employment status of the civilian population 25 years and over by educational attainment: http://www.bls.gov/news.release/empsit.t04.htm
According to this (last updated Dec 02, 2011) the not-seasonally adjusted aggregate unemployment for anyone who holds a HS diploma (regardless of higher level education) is 20%.
Edit: I didn't mean to cause any confusion by aggregating the "non-hs-dropout" stats, so let me make it clearer:
Level of Education : Unemployment Rate High School Dropout: 12.7% High School Diploma: 8.4% Some College/AA Deg: 7.4% Bachelors or Higher: 4.2%