Ben Armstrong published a much appreciated guide for installing Virtual Server 2005 R2 on a Windows Vista RC2 host:
There are two main parts.
First you need to configure IIS correctly. To do this you will need to enable to following subcomponents of IIS:
The second part is that you need to run Internet Explorer ‘as administrator’ by right clicking on it and selecting ‘Run as administrator’.
Read the whole article at source.