I have been messing around with the installation of Exchange 2010 RC on Windows 2008 R2.  I chose to go with Windows 2008 RC since it already has more of the things needed to install Exchange like the right version of PowerShell and the .NET framework.  To make my lab installs go faster I have been creating PowerShell scripts to automatic everything from the installation of the required roles and features to the installation of Exchange 2010 as well.  Below you will find some snippets from some of the scripts.  Of course the standard disclaimer applies.

The header:

# -----
#
# Script by Gerod Serafin - gerod dot serafin at microsoft dot com
# To run this script you will need to set the your execution policy to
# unrestricted using:
# Set-ExecutionPolicy unrestricted
# After the reboot of the server it will be set back to RemoteSigned.
#
# You may want to download and run the 2007 Office System Converter:
# Microsoft Filter Pack
# http://go.microsoft.com/fwlink/?LinkId=123380
# -----

The installation of the link above is so that the indexer can index certain files.

The following is needed for all Exchange installs since we are not using the old way (Windows 2008) of adding roles and features and are using PowerShell instead.

#Since we are not going to use ServerManagerCmd for this
#install we will need to add the Server Manager Module first on all installs.

Import-module servermanager

If this is the first time you have run Exchange 2010 setup, you will need to prepare the AD.  Before you can do that you will need to install the AD tools.  After running that a reboot may be necessary.  I have commented it out as I may want to see the results of the install.

#-----------START PREPARE AD NEEDS------------------------------------

#For a server that you have not done any Exchange 2010 prep
#you will need to do a /preparead.  Before you do that you
#will need to install the AD remote management tools.
#Uncomment below for that

add-WindowsFeature RSAT-ADDS

#Since this will probably require a reboot, you would need to run the #following:
#restart-computer

#-----------END PREPARE AD NEEDS------------------------------------

The next part does the AD preparation.

#-----------START PREPARE AD------------------------------------

#After the reboot you can run the following if you have a single
#domain and have permissions necessary to do it.  The /preparead
#switch will do everything needed.  Since I have an ISO of the
#Exchange 2010 RC on the D drive I change to the that drive first

d:
.\setup.com /preparead

#-----------END PREPARE AD------------------------------------

If your forest and domain is all prepared then you are ready to install the Hub and CAS role.  Since I wanted to get a DAG up and running I put these two roles on their own machine and put the mailbox role on two other machines.  The following will install the Features and Roles needed.

#------------START HUB and CAS INSTALL NEEDS--------------------------

#To install a Hub Transport Role on a CAS server, we would need to install #the following components:
#Net-Framework
#Web-Server
#WEB-ISAPI-Ext
#Web-Metabase
#Web-Lgcy-Mgmt-Console
#Web-Basic-Auth
#Web-Digest-Auth
#Web-Windows-Auth
#Web-Dyn-Compression
#NET-HTTP-Activation
#RPC-over-HTTP-Proxy
#Uncomment below for that (If not all on one line, make it so it is…)

add-WindowsFeature Net-Framework,Web-Server,WEB-ISAPI-Ext,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Basic-Auth,Web-Digest-Auth,Web-Windows-Auth,Web-Dyn-Compression,NET-HTTP-Activation,RPC-over-HTTP-Proxy

#The following service must be set to automatic
set-service NetTcpPortSharing -StartupType automatic

#------------------END HUB and CAS INSTALL NEEDS-----------------------------

Now that the server has what it needs, let’s install the Exchange portion for the Hub and CAS.

#------------START HUB and CAS INSTALL --------------------------

#Since I have an ISO of the
#Exchange 2010 RC on the D drive I change to the that drive first

d:
.\setup.com /m:install /r:H,C

#A restart will be required.  Uncomment below if you want this to happen #automatically.
#restart-computer

#------------END HUB and CAS INSTALL --------------------------

Now that we have a Hub and CAS role installed, let’s get some mailbox server installed on a different server.

#------------START MAILBOX ONLY INSTALL NEEDS--------------------------

#To install a Mailbox server, we would need to install the following #components:
#Net-Framework
#Web-Server
#Web-Metabase
#Web-Lgcy-Mgmt-Console
#Web-Basic-Auth
#Web-Windows-Auth
#Uncomment below for that.  (If not all on one line, make it so it is…)

#add-WindowsFeature Net-Framework,Web-Server,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Basic-Auth,Web-Windows-Auth

#------------END MAILBOX ONLY INSTALL NEEDS--------------------------

Now we are ready to install the Exchange portion of the mailbox role install.

#------------START MAILBOX ONLY INSTALL --------------------------

#Since I have an ISO of the
#Exchange 2010 RC on the D drive I change to the that drive first

d:
.\setup.com /m:install /r:mailbox

#A restart will be required.  Uncomment below if you want this to happen #automatically.
#restart-computer

#------------END MAILBOX ONLY INSTALL --------------------------

Hopefully this is useful to you.