Hi Aravind.
System is not letting you add them without division, because transaction 0100 (and 0200) can not be entered without a division. They are billing transactions and they need division.
You said you defined the division(s) you need in the above steps. You then also need to define them first in IMG - Financial Accounting(new) - Contract Accounts Receivable and Payable - Basic Functions - Postings and Documents - Document - Maintain Document Assignments - Maintain Transactions for IS-U, and then subsequentialy in EK01 and EK02 (posting areas R000 and R001).
Regarding your other question: internal transactions are used by SAP and are related to the process steps (define how specific programs run). By using external transactions and not specifying internal ones you can still define posting rules (by defining the posting specifications in the above mentioned IMG path, and by defining G/L accounts in EK01 and EK02). Im not sure what you mean by transactions for payments, since if its a payment that the system can identify then it will clear an open item, and if its not, it can, for example be a posting on account, which can then be handled by Main Transaction 0060.
Marko
