Windows Setup allows you to provide an answer file for a unattended install. Windows 2000/Windows XP had the winnt.sif but Windows Vista, Windows 7 and Windows Server 2008 allow you to provide a Autounattend.xml file. If you follow the right steps with SIM (Windows System Image Manager) and add the components the setup needs you can build a file which perform a automatic installation without any input during the setup phase.
Well I build such a Autounattend.xml file I run into the problem when the Windows Setup started I needed to choose which version of Windows Server 2008 R2 I wanted to install. This step I wanted to skip and really have automatic installation. To make that happen you need to add InstallFrom into the XML file.
<Value>Windows Server 2008 R2 SERVERSTANDARD</Value>
Make sure you query the WIM file with imagex.exe /info d:\sources\install.wim and insert that for MetaData Value (marked in RED).