You wanted to know how to install XBMC easy way, here is the steps on what to do on your Apple TV 2, to install XBMC from nitoTV
Things to Know:
1. Jailbreak your AppleTV 2 ( Tethered Jailbreak 5.2.1 )
Seas0npass http://youtu.be/bXvOJAH9KAo
2. Tell Difference Which AppleTV your Holding ( AppleTV 2 or The New AppleTV 3)
http://youtu.be/Ns1jMAhVa8Y
( If still confused, search google to know which one you have )