NT 4 Domain to 2003 AD question

Archived from groups: microsoft.public.win2000.setup_deployment (More info?)

I am planning a migration to 2003 AD from NT 4.0 Domain, right now I have
exchange 5.5 running on Windows 2000 server and also Cisco Unity server that
runs exchange 5.5 on NT 4.0 server. (Unity server does voicemail and
delivers it through outlook to people in the form of wav file attachment) I
understand that after I upgrade my PDC to 2003 and install AD I have to
install Active Directory Connector for my two exchange servers. What I do
not know is that am I supposed to install 2 ADCs one for each server or will
I need only one, and the second question is do I want to install ADC directly
on the servers or should I install it on another server(s)? Thanks for all
the help you guys can provide me with.