Excel 2007 : Inventory Tracker

I am doing an inventory of one of our stores and would like to create a worksheet with formulas to calculate items scanned.

One tab (Master Inventory) has all inventory on hand provided by the store broken down by:
Vendor, SKU (or barcode), Item Description, total on hand, total cost, and total retail.
I would like to have on another tab (Scanned Inventory):
Column A: SKU (or barcode) where I will scan the barcode
Column B: Item Description pulled from the Master Inventory sheet by searching for that barcode
Column C: The quantity scanned


I would like if I scan a barcode and it has already been scanned for the quanity to update and if not to add that info to the list on scanned inventory