Jean-Pierre Paradis's Blog: Windows Server 2003 Service Pack 1 modifies NTLM network authentication behavior

Microsoft Windows Server 2003 Service Pack 1 (SP1) modifies NTLM network authentication behavior. After you install Windows Server 2003 SP1, domain users can use their old password to access the network for one hour after the password is changed. Existing components that are designed to use Kerberos for authentication are not affected by this change.

Read the complete technote at Microsoft