Widescreen monitors that tilts to portrait mode will require Vista compatible drivers, if you want to use them in portrait mode.
is HDCP important to you?
I don't think HDCP is a requirement for Windows Vista certification. For example, video cards with HDCP capabilities are not advertised as "Windows Vista Certified". Yet such a video card would be necessary to display HD video on a monitor if the video content has copy protection.
I am not sure if I will be watching HDCP video on my LCD PC monitor in the near future. But that may be irrelevant anyway since I'm in the market for a 24"+ LCD monitor and they are all HDCP ready (to the best of my knowledge).
Jaguarskx- Unfortunately (now almost 2 years after your reply) not all HDTVs currently being sold are HDCP compliant. I recently emailed Olevia asking about the compatibility of their Digital Lifestyles 42" 720p LCD. They replied that none of their TVs are HDCP compliant. I've been shopping around for a few months now, and I've found that most TVs that are compliant list among their inputs '2X HDMI w/ HDCP', while most that are not compliant simply don't mention HDCP, hoping the question won't come up until after they have your money.