Welcome to Android Forums tobymack,
when your android device is plugged into your PC through USB Cable, it has to download drivers onto your pc to be read properly, if those drivers do not install you can search the samsung website for the drivers for your phone
im unaware of what a samsung looks like when plugged up, i do believe to to be the same on all android devices
you can simple select PC mode from the usb connections menu, and it will begin installing the drivers
or
Mass Storage Mode.
i hope this answers your question, and if not please let me know