S/Video won't work unless you down convert to 480i. You can record from an HDTV box onto an ordinary VCR-- it just won't be High Definition. (and the colors won't be sharp)
Long, long ago there were composite and Y/C separate standards for HD, but no home equipment ever incorporated them. You will [yes!] have to use a component, DVI, or HDMI connexion for HD resolutions unless you're working with some really exotic professional equipment, which might use SDI.