Its not that you wont be able to play HD movies of any resolution (480p, 720p or 1080p) but the problem is that if your card is not HDCP complaint, even in the highest HD resolution, the images where cinematography plays a vital role (the night scenes or dark scenes) will show a color spread effect.
Example: Here is a scene from Spiderman-3 which is shot in the night. See the color spread on the edges and specially because of smoke in the sky...