I was little worried when I found out that I would have to install Windows Server 2008 R2 to play with some of the Server based technologies (SharePoint 2010, EPM 2010, etc). I already had installed a Vista Business x64 6 months ago and It was performing good and my concern was that whether my existing installation of Vista will be retained or not? And subsequently will I be able to have choice of booting through either OS or not.
Finally i did installed Windows Server 2008 R2 today & fortunately, the results were very good. Installation was a very smooth procedure, took less then an hour and (I think) less then a dozen clicks. And my Boot Loader was automatically configured to give me option to boot through Vista or Server 2008 :)
Both Operating Systems are working fine.