From the manual page on the dbf functions:
There is no support for indexes or memo fields.
Hey! don't shoot me, I'm just the messenger. :-) You will probably have to export the dbf data to a text file and load in into PostgreSQL that way. Do you have access to the command line on the Postgres machine? The command-line utilities provide two different formats for loading data; you should be able to write out your dbf data in such a way that it can be imported directly via psql.
Further questions: How big is the longest memo field? Is there any "binary" data stored in memos, or is it just long text? What version of PostgreSQL are you using?