You can set the Windows 7 Logon screen to anything you like. Just select an Image which is less than 256 kb in size and resize it appropriately for your screen resolution.
First go to Run and type "regedit", without the quotes. This will open the registry editor.
Navigate to > HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Authentication\ LogonUI\Background
Double click the OEMBackground DWORD key and set the value to 1.
Now, paste the image which you chose earlier and copy it to >
C:\Windows\system32\oobe\info\backgrounds folder .
Rename the image to backgroundDefault.jpg
Restart your System and find your new Login Screen Background.