I recently posted about Exchange 2010 installation re-requisites on Server 2008 here, http://blog.exchangegeek.com/2009/07/exchange-2010-installation-tips.html. Anyway, with the imminent release for Server 2008 R2 (Windows 7) we should now use PowerShell to install Windows features due to Servermanagercmd.exe being deprecated in R2.
First we need to right click PowerShell and Run as Administrator, then import the Server Manager module in to PS using:
Import-Module ServerManager
Side note: If you want to run a script you should run this cmdlet to learn about signing them.
Get-Help About_Signing
Use the cmdlet Add-WindowsFeature to install the required features. I have provided typical examples below.

HUB
MBXadd-windowsfeature net-framework,rsat-adds,web-webserver,web-basic-auth,web-windows-auth,web-metabase,web-net-ext,web-lgcy-mgmt-console,was-process-model,rsat-clustering,rsat-web-server
EDGE
A restart is required to complete the install.