MS 2000 advance server

we are planning to migrate our PDC to MS server 2003, and trying also to make our existing 2000 advance server our BDC. for testing & learning purposes, we setup the MS Server 2003 and build simple GPO’s in its Active Directory. on the otherhand, we also setup the 2000 advance server, but when i try to install Active Directory, it results to an failure message that talks about something about ldap thing. in short, we r trying the 2000 advance server to a member of the 2003 server….. how can we resolve this