logon autentication

Hi i am using winnt server with sp6 and workstation are of nt with sp6,we have BDC installed in my local office and PDC installed in another office which is on WAN link.when a user logs in he gets autentication from PDC which is a wan link,how can iforce logon autentication from BDC, can anybody help me in this regards.

Thanks in Advance
Jaleel