Hadron,
Thanks a lot for your good reply. But regarding the retaining of the old PD I am kind of confused, You said I may loose my old pd if I leave the employer before filing 485 but I have seen many discussions including in murthy's website , which says that if the i-140 is cancelled because of the fraud or misrepresentation then one looses the pd otherwise once i-140 is approved then that PD belongs to the employee.Yes one has to start the entire process again with the new employer.I haven't read anywhere about the need to apply for i-485 to retain the PD.Please correct me if I am wrong.
thanks.