An invoicing form

I am using rails 2.3.11 and ruby 1.8.7 I basically need an invoicing form whereby I can select a customer name from an auto-complete text-box, and I want all the customer details to be automatically filled into all the other customer detail text-boxes upon selecting the customer name, leaving room for editing of those values. Similarly I want to select the products from an auto-complete text-box and I want the selection for quantities to change in relation to the product, the price to change in relation to the the product and size and the total to keep changing as I add remove or edit the products sizes and quantities,