I have a USB Bar Code Scanner interfaced to my Mac for data entry. First a scan of an id bar code is made. Then the operator has to tab, return or enter using the keyboard to advance to the next field wherein the scanner scans the chemical or supply being checked out. I am trying to find a way that FileMakerPro will automatically advance to the next field once the data is entered.

You should contact the company that made the scanner and see if it supports a modifiable "post-amble" character. I thought most of them did a return (which is not exactly the same as an Enter key on Macs, but usually works, at least in a dialog box; I find a dialog box to be a good mechanism for this, visual, modal, easy to continue).