1) Connect Xoom to your computer via a USB cable. (Not HDMI)
2) Xoom must be on or in sleepmode
3) Xoom will show up as a 'Media Device' much like a mp3 player. If you double-click on it, it will open up and all the folders you need are there.
You can copy files to and from the Xoom using the computer. You can not have more than 1 copy function going at any one time.
(I'm assuming they went with the 'Media Device' instead of an external drive, that way you don't have to 'safely remove' the device, because most people fail in that regard, and usually screw up their external data device)