From WinCustomize Wiki
LogonStudio Vista allows users to create, apply, and share logon screens for Windows Vista. Currently it only supports customization of the background image of the logon screen. LogonStudio Vista is compatible with both 32 and 64 bit versions of Vista, and it can be used with any version of Vista.
What LogonStudio Vista Does
By applying a 'logon' to one's desktop, you can change the appearance of your computer when you first turn it on and are preparing to sign into it. The logon applied will appear whenever the computer is locked or logged off.
How to Use LogonStudio Vista
To load a logon, double click any of the built-in logon screens to use backgrounds that are already loaded on your computer in order to apply the skin. Alternatively, you can single click the one you would like to choose and then click 'Apply' in the lower right hand corner. The built-in logon screens' wallpapers are located at C:\Windows\Web\Wallpaper.
Creating & Exporting Logons
In order to export logons, select the logon that you would like to export and choose 'Export logon package'. This will create a .logonvista file that you can upload to WinCustomize. Please ensure that you have permission from the wallpaper's author if it is not your own before you upload it.