Dual Exchange Servers

I have 2003 forest with two separate domains (Domain A.edu and Domain b.edu). Domain A has an Exchange 5.5 with the MX records for both domains. Domain B will be using a separate Exchange 2003 Server populated with the students only. How can we do the following (1) Have the users in Domain B indepedently of Domain A access and use the global address list of the Exchange 2003 Server. (2)Have the 2003 Exchange Sever global list available only displaying all the users in Domain B without causing conflict with the Exchange server in Domain A.