First up in my path to getting SharePoint 2010 running in a Hyper-V VM was the case of the missing roles in Windows Server 2008 R2, caused by a Windows update that failed to install.
For some unpleasant reason, KB971468 had failed to install correctly, following the cancellation of the install of KB890830 (the windows update panel had stopped mid-install, and the progress bar just stayed where it was). The outcome of this was that no roles displayed in the Server Manager - instead just an error message.
With the help of some worried searching, I came across this article by Glafkos Charalambous explaining the fix - use the System Update Readiness Tool from Microsoft to discover the faulty update files, then manually extract those files from the relevant update packages and copy them to the updates folder.
Once I had replaced the bad MUM files (wonder if there are DAD files anywhere in the system, too??), then I couls rerun the other updates that were marked as failed in the Windows Update History.
Hey, honey, I got my roles back!