First of all, High Definition content is not what you get on a DVD today. Most DVDs are 480i (upsampled to 480p by many quality players), the same as broadcast TV (but without the distorted colors). HD content is essentially everything above the 480 lines: 720p, 1080i, and 1080p (the last one is currently rare).

The upshot of all of this is that display devices need HDCP support. If a monitor or television supports HDCP, HD content will be playable on that device (provided that it hasn't been cracked). If a monitor doesn't support HDCP, one of two things will happen at the discretion of the content providers. It's a possibility that a given studio may simply refuse to allow the content to be displayed at all. More likely, the studios will allow for playback on unauthenticated devices with purposely degraded quality. The thinking is that Joe Consumer will be more likely to pay for HD content than seek out pirated content that's not in HD. Talk around the industry suggests that many studios will degrade content to a 480p level by passing it through a constrictor, although we won't really know until products start shipping.