We had already shared an utility which allows you to enable Snap feature in Windows 8 Developer Preview, and also shared free utility to change the background of Start or Logon Screen, if you are testing this version then you must noticed that Start Menu is changed, there is an green background which cant be changed.
Here is another free utility which allows you to enable Snap feature, Changed Start Menu background and Background of Start Menu, an user yvidhiatama at DA has created Windows 8 Dev. Preview Tweaker, which do all those for you very easily.
How To Use :-
Its an portable utility so you don’t need to install anything on your machine just extract the downloaded file and then run the EXE file and chose your desired options.