Crack dictionaries can be converted for use by npasswd . See the Npasswd Administration Guide for the conversion procedure. As many as you can stand. You can have multiple dictionaries, each generated from a distinct word list, or one large combined dictionary. A number of smaller dictionaries allows easier customization than one big dictionary.
More dictionary words equals greater password security.
It may also mean greater frustration in your user community because npasswd will reject more passwords. A. Several permutations are made on each dictionary word. Because the bad guys who are trying to get your passwords are using some very thorough tools like Crack. The dictionary check code in npasswd was written by the author of Crack, and performs the same checks. Given sufficient dictionaries, if npasswd accepts a password there is a good chance that Crack will not guess it.