Before matching the status of the po is unbilled or accrued.
When the po matched to the po status is chanhed to billed
and the balance in the accrued payable a/c transferred to
accounts payable account.
after matching with po u can validate the invoice and pay
them.then u can finally close the po so that it will not
appear in the list of value again 

thanks
srinibas
oracle_sri08@rediffmail.com