Logons are the screens you see when you are logging on to Windows.

Changing them manually is a painfull process, but you can download Stardock's LogonStudio to make things a little easier:
Stardock's LogonStudio(TM) is a free program that allows users to easily customize new logon screens for Windows XP.

You can download it here:

Windows XP Users Windows Vista Users

PLEASE NOTE: We cannot take any responsibility for changes you make to your computer. Installing files and making changes is at your own risk.

Here you can download plenty of free screensavers