THE PLT STATED HE WAS TOLD, THE R AUX FUEL PUMP WAS INOP & TO PRIME/START THE R ENG, HE HAD TO POSITION THE R FUEL SELECTOR (SEL) TO X-FEED. ON THE 1ST 2 LEGS OF THE FLT, HE USED THIS PROCEDURE, BUT NOTED THE R FUEL SEL WAS HARD TO MOVE. WHILE STARTING FOR THE 3RD LEG, HE WAS UNABLE TO MOVE THE R FUEL SEL TO X-FEED & GOT A MECHANIC TO MANUALLY REPOSITION THE SEL IN THE WING. THE MECHANIC RECOMMENDED REPAIRING THE ACFT BEFORE FLT. HOWEVER, THE PLT ELECTED TO LEAVE THE R SEL IN X-FEED & CONTINUE. IN FLT, BOTH ENGS USED FUEL FROM THE LEFT SIDE. DURING DESCENT, BOTH ENGS LOST POWER. SUBSEQUENTLY, THE PLT MADE A FORCED LANDING ON UNEVEN TERRAIN & THE GEAR COLLAPSED AFTER X-ING A DEPRESSION. AN EXAM REVEALED THE L MAIN & AUX TANKS WERE AT OR NEAR EMPTY, THE NACELLE & R AUX TANKS WERE FULL & THE R MAIN TANK WAS RUPTURED. THE PLT WAS UNAWARE THAT HE COULD HAVE X-FED FUEL FROM THE R TANKS TO THE L ENG. FUEL FROM THE NACELLE TANK MUST BE TRANSFERRED TO THE MAIN TANK TO BE USED. UNUSED FUEL/VAPOR FROM THE ENGS ARE ROUTED TO THE RESPECTIVE MAIN TANK.