If your Xoom does not appear under Portable Devices in your computer after you connect it to your Windows Xp/Vista/7, try troubleshooting using the assistant for your device:
You may need to update your computer's USB & PC Charging Drivers via Here. Make sure you have Administrator permission before installing drivers.
The USB driver is used for connecting your Xoom to a Windows computer via a USB cable.
The PC Charging Drivers allow you to charge your phone using your PC and a USB cable.