http://www.cdfreaks.com/news/Monitor-with-HDCP-support-required-to-play-HD-content-in-Windows-Vista.html
http://owened.net/2006/08/29/microsoft-cuts-hdcp-playback-from-32-bit-vista/
http://geeksaresexy.blogspot.com/2006/12/vistas-content-protection-badness.html
As a bit of a video geek I knew Vista was a turd before I could get my hands on a beta version.  If buying a new monitor try to find one without HDCP.  It might make things easier in the future... everything gets cracked eventually but if your display hardware has HDCP enabled crap it might not work.