Raspbmc is the Raspbian operating system with XBMC installed and set up so that it boots into XBMC.
This guide will explain how to install Raspbmc using the NOOBS (New Out Of Box Software) zip file provided by the Raspberry Pi Foundation on their download’s page. This guide will only explain how to install Raspbmc as the ONLY OS on the SD card !!
You will need an SD card formatted to FAT32 and either the NOOBS.zip file or the NOOBS Lite.zip file from the Raspberry Pi downloads page. The process is amazingly simple, once downloaded all you have to do is extract the .zip file onto the SD card using the program of your choice (Linux = 7zip/PeaZip/Ark/etc Windows = WinZip/7-Zip/PeaZip/etc).
Once this is done plug the SD card into the Pi and turn it on, it will start re-sizing partitions and creating new ones, when it is finished you will be left with 3 partitions on your SD card, the normal 2 and an additional recovery partition. You will be greeted by a selection of operating systems to choose from, select Raspbmc and click the “Install” button. You will see a warning appear about over-writing all existing data, click “Yes”, it will start installing Raspbmc on your system for you, sit back and grab a drink, when it’s done you will see a pop-up notifying you that the OS has been successfully installed, click “OK”.
The Pi will reboot and it will finish the final installation steps before rebooting once more. It will then start to patch the root filesystem, this can take a while please be very patient. Next it will download and extract XBMC before booting into it, choose your language and you should be at a screen similar to this one :
Raspbmc is now ready to use, plug in your USB stick/hard drive into a powered USB hub and start watching your videos/looking at photos and listening to your music using Raspbmc. If you want to enable add-ons and install repositories, etc in Raspbmc then check out this article.