Disconnect the antenna from the TV/VCR combo. Connect this antenna to the TV antenna connector of the DTV receiver. Connect a coax cable from the TV Out of the DTV receiver to the antenna connector of the TV/VCR combo.
You can easily hook up DTV to Tv/VCR combos by first buying a converter box. The older boxes which are VCR capable tend to be at your local home improvement stores such as Home Depot.