This is what official site says:
http://travel.state.gov/content/visas/english/general/ineligibilities.html
"(A) Conviction of certain crimes.-
(i) In general.-Except as provided in clause (ii), any alien convicted of, or who admits having committed, or who admits committing acts which constitute the essential elements of-
(I) a crime involving moral turpitude (other than a purely political offense) or an attempt or conspiracy to commit such a crime, or
(II) a violation of (or a conspiracy or attempt to violate) any law or regulation of a State, the United States, or a foreign country relating to a controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802)), is inadmissible.
(ii) Exception.-Clause (i)(I) shall not apply to an alien who committed only one crime if-
(I) the crime was committed when the alien was under 18 years of age, and the crime was committed (and the alien released from any confinement to a prison or correctional institution imposed for the crime) more than 5 years before the date of application for a visa or other documentation and the date of application for admission to the United States, or
(II) the maximum penalty possible for the crime of which the alien was convicted (or which the alien admits having committed or of which the acts that the alien admits having committed constituted the essential elements) did not exceed imprisonment for one year and, if the alien was convicted of such crime, the alien was not sentenced to a term of imprisonment in excess of 6 months (regardless of the extent to which the sentence was ultimately executed)."
So, as I understand it, even with a case involving turpitude, where the maximum penalty do not exceed 1 year, and a sentence assigned is less then 6 months, one would still be eligible.