TWO OF 3 REQD FLT ATTENDANTS (F/A'S) WERE DISTRIBUTING PASSENGER (PAX) COATS AS THE ACFT WAS BEING TAXIED AFTER LNDG. SMOKE FM AN OVERHEATED AIR COND (A/C) PACK BGN ENTERING THE CABIN & THE F/A'S RETURNED TO THEIR DUTY STATIONS. THE FLT CREW STOPPED THE ACFT AT THE GATE & SHUT DWN THE ENGS, BUT LEFT THE APU RUNNING TO PROVIDE ELECTRICITY FOR LIGHTING. THEF/A'S OPENED THE L FWD DOOR & GND PSNL OPENED THE REAR STAIR DOOR TO DEPLANE THE PAX. THE CAPT MADE AN ANNOUNCEMENT TO KEEP THE PAX CALM, BUT SMOKE BCM DENSE & PAX OPENED THE EMERG EXITS OVR THE WINGS & BGN EXITING FM THEM. TWO PAX RCVD MINOR INJURIES WHILE EXITING OVR THE WINGS. AN INVESTIGATION REVEALED THE ACFT HAD BEEN DISPATCHED WITH THE R PACK COOL-ING FAN INOP AS AUTHORIZED BY THE MIN EQUIP LIST (MEL). DRG FLT, A RADIO INTERFERENCE FILTER IN THE A/C SYS FAILED WHICHALLOWED THE FWD PACK SHUT-OFF VALVE TO OPEN, BUT NOT CLOSE. THIS PERMITTED APU AIR TO RUN THE AFFECTED PACK EVEN THO THESWITCH WAS OFF & A CIRCUIT BRKR WAS PULLED. WITH THE ENGS SHUT DOWN & THE R COOLING FAN INOP, THE SYS OVERHEATED.