About Org unit Dates

Hi Experts,

Plz clear my doubts. in OM.

i want to change the one org unit starting date. And i assigned wrong position number for a emp... i want to change the position number.. how to do it? plz help me...

How many number of SAP HR Sub Modules are available... Like OM, PA, PD, Time ..........

like this i want to know the number of the sub nodules in SAP HR....

Thanks in advance

Balaji