Drivers & SDK
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Drivers:
If your'e on a Windows PC, you're going to need some USB drivers so your computer can talk to the Xoom in it's different operating modes (fastboot, rsd, and USB debugging).
You can get these drivers here:
For 32bit versions of Windows:
MOTODEV > Documentation & Tools > USB Drivers > Handset USB Driver for Windows (32-bit)
For 64bit versions of Windows:
MOTODEV > Documentation & Tools > USB Drivers > Handset USB Driver for Windows (64-bit)
*Note: Mac OS X & Linux don't require USB drivers.
SDK:
(If you already have the Android SDK installed with tools & platform tools you can skip this next section)
If you want to download the Android SDK, you can do so here:
Android SDK | Android Developers
If you don't plan on developing software and just want the few files needed for unlocking and rooting I have attached them to this post as sdktools.zip. Just download this and unzip it. You will have an sdktools folder that contains just fastboot, adb and AdbWinApi.dll.