Product Search

Thank you in advance for any assistance you be able to provide.

I would like some help on searching for product codes or serial numbers and formatting this into an order form a current customer form.
I have 4 main tables

CustomersID (PK)– Name, Address, City, Post Code, Tel Number
OrdersID(PK) – CustomersID(FK), Order Date,
OrderDetailsID(PK) - OrdersID(FK), ProductID(FK), Quantity
ProductsID(PK) - Code Number, Serial Number, Description, Color, Unit Price

I think I have all of these linked correctly

Here's what I am trying to achieve (so far with little success)
I have a customer form that I fill in name address etc; I then have a button that will take me to a customer order form, easy so far.

In my product table there are about 2000 separate products (spare parts for electrical appliances) so what I would like is for a popup box to appear when the order form is loaded (as a drop down or combo box isn’t practical ) so I can search for the product by code number or serial number only for a particular spare part. The description and price are fixed in the products table and should not be changed on the customer order form, I would then like the selection of the code to transpose to the order form.

In other words I would like when the code number has been entered and the product found that the info should then be added to the order form (model or serial number, part description, color and price all taken from the products table) I would like it that when the product has appeared on the order form that it cannot be changed, only by being deleted.

I know this appears to be rather basic but for some reason I am hitting a brick wall, I have looked at many db's and even tried to dissect Northwind to do what I want but cannot make it happen, now after 8 days in the wilderness I need help or guidance.

Thanks in advance
Kim