Can't find Viridian in your Windows Server 2008 RC0 ??
Can't find the Windows Server Virtualization role in your Windows Server 2008 RC0 build?
Look for the Viridian bits under c:\windows\wsv and install the bits in order you find there.
After which, you'll find the roles listed in the Server Management.
For more details, check this blog from the virtualization team. http://blogs.technet.com/virtualization/archive/2007/09/28/windows-server-2008-rc0-and-virtualization-ctp-faq.aspx
/Dennis