Insert Problem

Hi  All ,

I have 2 tables

Organization and  Customer Table

Organization table columns

orgid it's a primary key not an identity column,

firstName ,lastName

Customer Table

First Name,Last Name

am issuing this  query

.......................................................................

insert into organization(firstName,lastName)

select  firstName,lastName

Error is as there already primary key am not able to insert a record . The Organization table has serial no 1 - 187 number

in the orgid table . I  want to insert records in that table with this script only .Please help in altering this script so new number can automatically be inserted after the existing max no

Kindly suggest me

Thanks