Inventory Valuation

Hi All,
I am trying to value inventory on FIFO basis (atleast to nearest possible accurate level). I have exported & doctored few reports from Quick Books (accounting s/w). On attached sheet on FIFO details tab I caputred on hand inventory, received between 7-1-09 to 8-18-09 PO by PO details on PO cost tab with other cost overhead items broken down. what i would like to do.. on FIFO details tab- for on hand inventory- find rate or average rate starting from the last received PO. see example shown on line 11 on FIFO Details sheet. can any one provide any code or formula to achieve this? # PO received column does not have much significance, since i was trying to check how many po's are making the total received qty's. Please help
SD

attaching the file sample data