If you are feeling bored with your dull old login screen then you can try LogonStudio. LogonStudio is a freeware utility that allows you to change the login screens of your Windows XP machines. LogonStudio comes with several predefined logon screens. There is also an editor to create your own logon screens. LogonStudio Vista will help you to modify logon screens for Vista.
You can also choose to display random Logon screens for each login with LogonStudio . With the built-in editor you can easily modify them. You eitehr build or edit the logon screens by just changing some parameters in the editor panel. There are also many logon screens that you can download from WinCustomize.com. As the application is totally free you can give it a try.