VBA to look up part number when scanning a barcode

I have a USB scanner connected to a PC. Data is entered into Excel when the part number barcode on a box is scanned. I have two worksheets that I will be scanning part numbers into, one is Group A and the other is Group B. On Group A's sheet there is a list of Group B part numbers that will be used for the lookup procedure when the barcode is scanned. The same is true for Group B's sheet. The groups should never be mixed, so if part number "B005" is scanned into Group A's sheet it should cause an error message to pop up. I've attached a workbook as an example. Is it possible to do this with VBA?

Thanks

Barcode Scan Lookup.xlsx

OllyXLS, since VBA is very new to me, I'm not sure how I would go about adapting the code you wrote.