CVG Controller experienced a loss of separation event when issuing a descent clearance through an occupied altitude; the reporter listing the distraction of assisting with an INREQ as a causal factor.

Narrative

I was working all RADAR positions combined to the Tower. The C182 was at 7;000 FT level and passing through my airspace. The A320 checked on my frequency with intentions of landing at CVG. I issued a heading of 310 and altitude of 8;000 FT. I was also performing CIC duties and Dayton FSS had called with an INREQ for an aircraft overdue to an airport in my airspace. I turned around to the TMU station trying to figure out how to work some of their equipment to see if I could locate that aircraft. The A320 asked for lower; I turned around; walked to my scope looked right at the situation and issued the A320 a decent to 3;000. I looked right at the scope and thought the two aircraft had passed. I was back at the TMU station when the Conflict Alert sounded. By the time I looked at the situation again I determined that the aircraft were going to miss but with a loss of separation. We have a piece of equipment here nicknamed the 'fish finder' which is what I was trying to find at the TMU station. I have not been trained on the use of this equipment so maybe if I had had that training then I would have been able to quickly help the FSS with their INREQ and been paying closed attention to my traffic.