Northwest Flight 78 (NW78), a B-757, was parked at Gate 17 facing east with Mobile Passenger Lounge (MPL) docked at L1 door. United 52, a DC-10, taxied in easterly direction by left side of NW78, then turned right to southeasterly heading to follow lead-in line to Gate 15. DC-10 was on lead-in heading with nosewheel about 3' to 6' right of line & following signals from guideman, when right wingtip struck aft end of MPL. Driver of MPL was standing on gangway & fell backward into 757 & received minor injury. Both planes received minor damage; MPL was substantially damaged. United had recently begun to use Gate 15 for DC-10's. At that time, NW was using DC-10 on Flight 78, which deplaned thru L2 door, but a week before incident, DC-10 was replaced with 757 that normally deplaned thru L1 door. NW78's arrival was late that day, so deplaning was still in progress when Flight 52 arrived. Measurements confirmed insufficient clearance existed for DC-10 at Gate 15, when MPL was docked with 757 at Gate 17.