Helena,
Welcome to Lactnet and to NYC.  I also live and work in NYC, with a very mixed
population of moms.  (Everything from homeless shelters to high income
professionals).  Some observations of the African-American and Hispanic
populations in NYC:
Many moms from the low-income African American population in NYC are single
moms.  This does not mean that the father is not in the picture, often he is
very proud of and involved with the baby, but does not marry or live with the
mother.  The greatest barrier to breastfeeding among this population seems to
be peer support, as it is important to African-American moms that they have
female role models for breastfeeding and mothering behavior.  There is an
article on significant others and the effect on the decision to bf in June
'95's Journal of Human Lactation that you might find helpful.  Peer counselor
programs have been very successful among minority, low income moms.
        Empowerment is another important issue.  If a woman was abused or
otherwise disempowered, it is more difficult for her to trust her body to
produce milk.  I have found that carefully explaining body functioning
(adaptations to pregnancy, breastfeeding physiology-supply/demand, etc.) in a
way that fosters an appreciation for the healthy female body during pregnancy
facilitates this trust.  Teaching the reasons behind all the neat things our
body does, how each "symptom" is indicative of a healthy process, and how the
mom can co-operate with the process rather than the typical patriarchal view
of the pregnant body as delicate and problematic seems to be the key.  For
example:  rather than saying that pregnant women get constipated, I say that
the rate that food passes through the intestines slows down during pregnancy,
to provide more time to absorb nutrients.  Getting exercise, drinking plenty
of water and eating fresh whole foods for fiber co-operates with this process
and prevents constipation.
        Hispanic moms are often reluctant to breastfeed in public, and can
wind up weaning early due to early bottles given while entertaining guests.
Hispanic moms who have been born in the US seem to have lost the
'breastfeeding culture' and many do not even consider breastfeeding an option.
 Many know no one who has breastfed.  Some of these moms will later express
regret about not breastfeeding when they learn of the benefits of
breastfeeding.  In this population education on the benefits are valuable, as
well as teaching directed at discreet breastfeeding.  Peer counseling or La
Leche League meetings provide role models.  Hispanic fathers are also likely
to object to the baby nursing from "his" breasts.  Mothers-in-law are
important and can be a blessing or a curse, depending on their supportiveness
and knowledge.  I have found minority mothers to be no more likely to decide
against breastfeeding because of the need to work than 'white' mothers.  Moms
either know one can pump, or they do not even consider it.  Low income moms
might be more likely to mixed feed when they return to work or school, as low
paying jobs are less likely to provide privacy and breaks neccessary for
pumping.
        Teen moms are more likely to be of minority ethnicity in NYC.  A
salient point to breastfeeding promotion among teens is that breastfeeding
allows the teen mom to be the baby's mother, prevents the grandmother from
taking over.  This can be a selling point for some teens, and a turn off for
others.  Depends on whether she wants to mother her own child or not.
        These observations are (of course) generalizations, but might be
valuable in your work.
Good luck.
Catherine Watson Genna, IBCLC
PS- My 'baby' sister graduated from Cornell 2 years ago.