As I said earlier, one of the most exciting features of Windows 7 is the customization capabilities it offers to users. One such feature is its ability to change the Logon Screen background without patching the system.
There are several such free tools available for download (find some of them here), here is a new one called 7 Logon Screen Manager.
This is a portable tool that means no installation is needed, just run it, select a folder that contains images or select an image, which you would like to see you as logon background.
You can restore to default logon in windows 7 anytime with this utility itself. This is a System friendly edition; it means it doesn’t patch any system files. It just deals with the service which exists in the system. 7 Logon Screen Manager can be downloaded at source.