Just look at the new cable box
How is it connected to your tv
Does it have A/V connectors
From statements in your post...seems you are still watching SD tv on a tube type set, recording SD tv on your vcr
Either that cable box is going to have analog VIDEO output for your old tv
Or you are going to need a new hdtv
IF it will connect to the old tv, it will connect to the old vcr
Either it works or you are forced to upgrade everything
If you have a new HDTV why are you still recording SD tv on a vcr ?