Hi jfoxtrot,
As Jakewash has suggested, you'd be better off using the component video output from your cablebox. By the way, it will be years away before cable and the broadcasting systems go to 1080p because of the bandwidth requirements and the installed base of 720p/1080i broadcast equipment.
And don't assume that the HDMI connection will deliver better picture quality than component video. On my Scientific Atlanta box (8300HD), the component video output delivers a better image than the HDMI output into a native 720p display.
Regards,
Alan
