I have no idea about the AM2/3 retention brackets. But if you were to get the DK, you would just need the Thermal Paste, and only if you don't like the stuff they include(not a pad obviously). You can use rubbing alcohol to clean your CPU. again since I am unfamiliar with AM2/3 I can not be sure if it includes everything for AM2/3, most likely it does.
Stuff in package(click to enlarge)http://img6.imageshack.us/img6/1126/3523302918.th.jpg