The Read-only Domain Controller is one of the new and most existing features of Windows Server 2008. So is Server Core. Combining these two features opens up a whole new world of possibilities for your Active Directory environment.
Server Core Domain Controllers are the high-performance low-maintenance brothers of Domain Controllers running on full installations of Windows Server 2008. I've already showed you a long time ago how to install Server Core Domain Controllers. (the post that started the Server Core frenzy on my blog over a year ago) Now I feel it's time to show you how to add Server Core Read-only Domain Controllers to your existing Windows Server 2008 domain.
This blogpost contains the following information:

• Reasoning
  • Reasons to install additional Domain Controllers
  • Reasons to install Read-only Domain Controllers
  • Reasons to install Server Core RODCs
• Preparations
  • At least one Windows Server 2008 Domain Controller
  • Domain and Forest functional levels
  • RODCPrep
  • RODC Compatibility Pack for down-level clients
  • Active Directory Sites
• Installation Method 1 (Scripting)
• Installation Method 2 (Answerfile)
• Installation Method 3 (Staged Deployment)
• Installation Method 4 (Install from Media)
• Concluding

Read the guide.