If you intend to place cabinets or built-ins in the location where the existing radiator is located, you have a few options available.
For heating only, you can replace the old radiator with a toe kick radiator. This style radiator fits under the cabinet within the toe kick space and has a blower to push the heat out into the room.
To supply both heat and cooling, you should look into a mini split system by either Mitsubishi or Daikin. They have many different configuration of air handlers from small radiator style to in-wall units as well as surface mounted units typically used in retrofit installation.
For more information:
Read Randy Potter's Q&A "I can't afford geothermal. Is an air-to-air heat pump my best option for heating?"