Conditional V Lookup at multiple lines

The question may sound naive since i am not sure whether this functions. But following is the output i am looking for.

Sheet 1 i have item code, item description, stock quantity at the year end date.

Sheet 2 i have purchase details of all items during a financial year. An item may be purchased only once or more number of times. Every single purchase transaction is depicted at separate line. i want to fetch the value of v lookup quantity of last purchases which will match or be greater than the stock quantity.

E.g. Item A is having stock quantity 10 in sheet 1. To fetch the last purchase date i have sorted sheet 2 in descending manner on dates. Thus by logic last purchase is fetched as say, 11th dec 08 with 3 quantity. Now still i am short with 7 quantity to match the stock. Hence i want to fetch next transaction which will match with the balance requirement or again will go for next transaction.

is the above manageable with vlookup or something else ?

thanks in advances.

As you would observe from the attachment, I have stock quantity in sheet 1 against each item. I have purchase transactions for all items in sheet 2. Now stock quantity in sheet 1 is 27 as at 31-12-08. With FIFO method i want to identify which are the purchase transactions of which stock is lying. Thus document number 967 (qty 8), 789 (qty 15) & 567 (qty 10) will qualify this logic.

i would like to either
populate all such three purchase transactions in sheet 1
or highlight three of them since they qualify
or total all those three purchase quantities and call them in sheet 1 against that item code
or any other feasible solution you might think of.

My objective of doing the whole exercise is to find out inventory ageing. is it possible by any chance ?

thanks in advance.

Any solution possible for this query ?