Look in the AVSforum.com HTPC section and bottom line is you CAN'T future proof a PC for HD playback.
HDCP is an attachment to HDMI, its bidirectional where the source sends a query of some kind to the next device in the video path, and if that device can't authenticate, the source only sends standard definition video to it.
The real catch is that the people behind HDCP are paranoid, so right now it looks like ONLY 100% original PCs from a few brands running VISTA will get approved. No changes to the video path, which is a protected encrypted "tunnel" in VISTA will be permitted.
Double Whammy, Pretty much everything shipping right now in HD is NOT going to be compliant (that new $5k display included), which would make consumers revolt, so content providers are planning on not setting the HDCP protection flag for the first 6 months to a year, then time to buy new stuff.