It sounds like the bar code scanner that you have uses a "keyboard
Wedge" interface. This means that the bar code scanner works like a
second keyboard attached to your PC.
The scanner should have come with a users manual containing a number
of special programming bar codes that you can scan to enable and
disable different functionality. What you want is to program the bar
code scanner so that it adds either an Enter keystroke or a TAB
keystroke after each bar code that you scan. In Excel Enter moves the
cursor down to the next row and TAB moves to the right one cell.
In the bar code scanner users manual, this feature would be called
something like a "Suffix" or "Postamble" keystroke. If you cannot
figure out what bar codes to scan in the users manual, call the
manufacturer and have their tech support department tell you how to
configure the scanner.