How To Use Lookup Function With Multiple Criterias

I've forgotten all the formulas that I learned during college. And that was for Excel 2003; now I'm using Excel 2007. So, hopefully you experts can help me out.

So here's the problem. I need to set up an invoice in Excel but I don't know what formula to use. I'll first describe my invoice and then I'll tell you the problem.

It's a basic invoice where you have customer's info and product's details and prices. So, when I choose a customer's name from a list in a cell, the address and phone of that customer will automatically appear. I don't have a problem at all with this part. And then there's the product details section where you enter a product type, size, color, price per unit, and total price. The price per unit also depends on the customer entered. Each customer has different pricing and I used a discount system for each customer. We basically have a universal price list for our products, but we have different discount percentage for each customer.

My invoice will look something like this: ...