How to integrate MS Office applications

When I need to produce an invoice, I have to update each of 3 Excel worksheets (Invoices due, marketing & milage analysis, stock & expenses control), a Word document (database of clients used for mailshots), create the actual invoice in a Word document, and print a compliments slip which is in a Publisher document. Some data has, therefore, to be entered more than once. Is there any way to speed this process up and make it harder for me to forget one of the steps in the invoice creation process ?