unable initialize dao/jet db engine

Howdy all:
I can't able open the database using DAO,but ADO can, it
prompt "unable initialize dao/jet db engine", why ? Which
component i should add? I guess that the Access open
database through DAO, so I install it, and the Access
application can open the database *.mdb, but my
application still not, who can tell me which engine does
the Access use, DAO,ADO or OLEDB?What relation of them is?
Thanks!