"HD" usually refers to videos, not video games.
The quality of your video game isn't just limited by the resolution, it's also dependent on all the quality settings within that game.
Basically, if you ONLY had support for 1024x768 and could crank up all the quality settings including 8xAA or higher the game would look pretty good which may be more in line with what you are asking.
Low quality on your screen won't look that great.
However, a high quality video on your screen would look quite good. My dad has a RIM Playbook with a width of 1024 pixels. We tested it and I ripped a BluRay to it (movie ripped to 1024x567) then we put that out to an HDTV via the HDMI cable and it looked really great. Not quite as good as a full 1920x1080 movie but still quite good.