A/D Beginner Question
All you need is a resistor divider:  

  

If Vin = +5 V then Vout will also be +5 V. If Vin = -5 V then the divider will set the output voltage nicely halfway between the two voltages, so that will be 0 V. So this scales [-5V, +5V] to [0V, +5V] for your ADC.  

To get the data in your PC you'll need a microcontroller with USB on-board, or a UART-to-USB bridge like this one. If you install FTDI's virtual COM driver on your PC the USB connection will serve as a transport channel for UART data.  

edit
If your sensor only needs a few mA you can use this charge pump converter to generate the -5 V from the +5 V USB supply: