Windows 7 has lots of customization options of which support for Changing Logon screen Background is given natively but that would require you to change some parameters in registry editor. This can be avoided and procedure can be automated using a small tool that lets you change Logon Background image on the go.
Windows 7 Logon Background changer is a name of the utility allowing you to choose the images of your choice and set them as Logon Background. Also, this tool lets us adjust the shadow of the text of the welcome screen, so as to ensure that it remains readable and clearer than the background image (the text of the home screen is white).
This application is made with the Windows Presentation Foundation, through which gives us a rather spectacular and intuitive interface. It is open source, and it works perfect in the Windows 7 RC as in the RTM version.
Download Windows 7 Logon Screen Changer
What is that rainbow wallpaper? I love it!