Depends, do you have a partition defined with MAXVALUE? If so, you have to split the maxvalue partition:
ALTER TABLE xyz SPLIT PARTITION part_max AT (to_date('02/01/2002','mm/dd/yyyy')) INTO ( PARTITION part_jan, PARTITION part_max);

Otherwise, you can just add a partition:
ALTER TABLE xyz ADD PARTITION part_jan VALUES LESS THAN (to_date('02/01/2002','mm/dd/yyyy'))

If you are using local indexes, they will be maintained with the addition of a partition. http://technet.oracle.com/docs/produ...2a.htm#2054899
for reference.