I do a LOT of Exchange implementations and even at that it's hard to remember the exact prerequisites for every combination of roles and services for Eaxchange. With Exchange 2010, Microsoft has included a scripts directory with XML files for pretty much any scenario.
You'll still need to do a handful of manual tasks, like ensuring the NetTCPPortSharing service is set to automatic (it's manual by default), but XML files in the scripts directory will take care of all the roles and features you'd usually install through server manager. There are options for:
- All roles - Exchange-All.xml
- Typical - Exchange-Typical.xml
- Edge - Exchange-Edge.xml
- Client Access - Exchange-CAS.xml
- Hub Transport - Exchange-Hub.xml
- Unified Messaging - Exchange-UM.xml
- Mailbox - Exchange-MBX.xml
To use these scripts, open a cmd window as an administrator and run "ServerManagerCMD -ip <full path to xml file>" and the appropriate bits will be installed.