If they are both in the same site,
-it's the first one to reply that authenticates...
-you can't change replication schedule, cos as soon as one changes it replicates within 5 mins (if all it well)...
you can specify one or the other as preferential for authentification by changing the DNS records
something about priority or weight on the SRV records.... can't tell you exactly what off the top of my head tho.. sorry.
if not in same site..
yes you can control replication, and each one deals with clients on own subnet....
Aftertaf (david)
MCSA 2003