Excel 2003

Have created Sales Order with Drop Down List for Customers (31) and Products
(12). Invoice # is automatic as is Date. Workbook has worksheet for each
Customer. Challenge now is to capture the sales data on the correct Customer
Worksheet. I could go and buy a software package for all of this; but where
is the challenge in that?

Need to capture the usual:

A1 Date, B2 Customer Name, E2 Invoice #, B4-B13 Product, C4-C13 Quantity,
E14 Shipping.

Being somewhat of a novice on the vast array of functions and their use, I
am sitting here wondering how to start.
I have scanned all of the subjects and threads and see nothing that jumps
out. I believe there may be a number of ways to approach this and would like
to be pointed in the right direction, learn what i can, and ask questions as
I go. Thanks in advance.
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Thanks from Salt Spring