Assuming the postgresql database is up and running and fairly functionaly, you should try dumping it in seperate schema and data files and editing accordingly.
pg_dump -s database
will output the schema. Since postgresql schema includes things MySQL doesn't know about, like sequences et. al., you'll need to edit it to remove those references and change data types and such.
pg_dump -ad database will dump the data only in insert format. That should import fairly easily once you get the schema changed.
For changing the pgsql calls to mysql just search and replace them, and don't forget to add mysql_select_db statements, since postgresql selects databases in the connect string. Note that the format of something things is reversed. In postgresql, the pg_query command is laid out:
pg_query($query) OR
pg_query($conn,$query)
whereas in MySQL it's the other way around for the conn / query.
