Once you've downloaded the img.xz file, in my case it is titled BBB-eMMC-flasher-2013.05.08.img.xz, you'll need to extract the archive. To extract the archive, you'll want to download and install 7zi
p. 7zip is a free and open source utility that is able to extract img.xz files (among many other file types!).
It will take a minute or two to extract the file, and you should then end up with a 3.66 GB .img file (notice that the .xz is removed from the file extension).
Next, download the free Win32 Disk Imager
software that we'll use to copy the image to the microSD card. After downloading the software, extract it from the zip file (7zip can be used here as well).
Launch the Win32 Disk Imager Software by double clicking the "Win32DiskImager" file in the folder that you extracted it to. You should see the following screen once it launches:
Click the folder icon (arrow pointed to it above), and choose the image file, and click Open:
Next, insert your SD card, and choose the correct "Device" drive letter. You may want to open windows explorer to help figure out which one to choose. Another way is to view the drive letters by clicking the dropdown below "Device", and then inserting your SD card to see which one gets added to the list.
Once you've made your selections, click the "Write" button illustrated above, and wait for it to complete writing to your SD Card.
You can now continue on to the Flashing the BeagleBone Black
page to continue.