I've tried adding a combo box to the contact database that came with access. (I'm trying to add "salesperson.") When I click on one of the names on the drop down list, it puts that same name in all the records. I've tried putting in my own values and having it look up the values in a new table I created called "salespeople." I also tried adding another column to the contacts table and having the combo box look there, but it does the same thing no matter what. What am I doing wrong?

You need to put that combo box in the table that the form is based on. Because it is an unbound field it does not know to link that selection to only one customer.