1. Open the registry, and find the key below. 

2. Create a new DWORD value and name it 'PasswordExpiryWarning' set the value to equal the number of days at which the Password Change Notification is presented. 

Key:[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
Value Name: PasswordExpiryWarning
Data Type: REG_DWORD
Data:(Number of Days)
More info: http://support.microsoft.com/support/kb/articles/q135/4/03.asp