You are the messaging engineer for your company. You deploy a new Exchange Server 2007 server named Server1 in your existing Microsoft Exchange Server 2003 organization. You need to plan for the creation of recipients on Server1. What should you recommend?

A.
Use the Exchange Management Console.

B.
Use Active Directory Users and Computers.

C.
Use the Set-CASMailbox cmdlet from the Exchange Management Shell.

D.
Use the Connect-Mailbox cmdlet from the Exchange Management Shell.

Explanation:
EMC > Recipient Configuration > Mailbox > New Mailbox…

Rules for choosing Exchange 2003 & 2007 mixed-mode management tools:

1. Use ESM for any tasks performed against 2003 servers.

2. Use EMC or EM Shell for any tasks against 2007 servers.

3. Use EMC and EM Shell to make organization-level changes, unless these involve features discontinued in 2007, such as administrative or routing groups.

4. Use ADUC to create or modify mailboxes stored on 2003 servers. You cant use 2007 tools to create 2003 mailboxes because the RUS is absent.

5. Use EMC or EM Shell to create or modify mailboxes stored on 2007 servers. In 2007, Mailboxes possess attributes not present in 2003 mailboxes. If you use ADUC to create a 2007 mailbox, only the 2003 properties will be enabled, preventing full functionality.

http://searchexchange.techtarget.com/generic/0,295582,sid43_gci1286930,00.html#creating_mailboxes_RUS