User Account is getting locked out after a password change on Domain Controller Active Directory. Why?

Hi,

My account is getting locked out on a daily basis. I have seen that the DC logged an event saying Sharepoint tried to logon, but had an incorrect password.  I am sure it is due to the passwords not being synced between DC Active Dir and Sharepoint as this has been happening since we changed our passwords.

Could someone tell me if you have to manually sync passwords, run an stsadm command to sync these passwords. I would of thought this was automated. Could it be I haven't got a service running which does this?

Can you help? 

Thanks.

John.