Of course it will work in Filemaker 10. I'm not sure if using a lookup is the best way. I believe having these items in a related table and placing an order portal on your customer layout would work smoothly. Fields in the portal would include item number, description, price, and whatever else. Rather than a pull down menu to find each item, you could use the auto-complete option with the script trigger- OnObjectKeystroke to watch for use of the Enter or Return key which would complete the selection, display the item information, and go to the next portal row.
You could also use another portal on the layout to sort through all inventory items allowing you to find items when you and your customer don't know an item code.
There's much more you could then do such as pulling the items from inventory, totally the order, printing it as an invoice, etc.
So each customer would have their main table occurrence, a related table occurrence for orders/invoices/payments, etc., and a table occurrence for inventory, and much more.