Should be just the HDMI. Most tvs have a input selection in the menus somewhere or others automatically choose the input that provides the best picture. Also make sure you choose, if its not automatic, the highest resolution, either 1080i or 1080p.
hdmi should be the only cable you need between the cable box and tv. Disclaimer: We just dealt with this about a week ago, and it worked that way here in oc, so cal... using cox cable. Your mileage may vary.
I have A Panosonic. I never use the feature (it splits the TV into 2 screens). To be honest, don't really know how to work it well. Besides, it's just too irrating for me.
Over, you can use that HDMI port for a laptop or pc, too.
Like watching netfix movies, or youtube vids, etc.