I looked up "lard" on Babelfish. I'm not sure which version of Spanish Babelfish favours, but it provided "manteca de cerdo". So far as I can tell from my visits, "manteca" is used in Argentina to mean cow butter, but in Mexico and Spain, "mantequilla" is used for butter. Then I found this definition for "manteca" on Wikipedia:
http://es.wikipedia.org/wiki/Manteca

However, "pork fat" differs from "lard", I think, in English, so would the corresponding Spanish terms be "grasa de cerdo" for pork fat and "manteca de cerdo" for lard? And would the latter term be used even in Argentina?