TURBOJET ACFT WITH ANTISKID SYS INOP LOSES CTL WITH BLOWN TIRES AND DEPARTS RWY LNDG AT DEN.

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THE PIC WAS IN THE L SEAT AND I WAS IN THE R. ANOTHER PLT WAS ON THE JUMP SEAT. THE PIC HAD REQUESTED WE ACCOMPLISH AN AIR DRIVEN GENERATOR TEST DEPLOYMENT ON THE WAY DOWN FROM ASE TO DEN. WE WERE GOING TO DEN FOR ROUTINE MAINT. THE PIC BRIEFED THE OTHER PLT AND MYSELF THAT IF WX WAS NOT VFR; OR IF TIME DID NOT PERMIT ON APCH; WE WOULD NOT DO THE TEST DEPLOYMENT. WX WAS MARGINAL AND WE WERE ESTABLISHED ON THE ILS IN VISUAL CONDITIONS AT APPROX 6 MI FROM THE RWY WHEN THE PIC ASKED US TO ACCOMPLISH THE TEST. THE PROC WAS ONLY ABOUT 1/2 DONE WHEN WE REACHED THE RWY AND THE PIC DECIDED TO LAND THE AIRPLANE. BOTH ENG GENERATORS WERE OFF LINE AS WELL AS APU GENERATION. ELECTRICAL PWR WAS BEING SOLELY SUPPLIED BY THE AIR DRIVEN GENERATOR. ANTISKID WAS NOT OPERATIONAL ON AIR DRIVEN GENERATOR PWR; SO AFTER TOUCHDOWN; WHEN THE PIC APPLIED THE BRAKES; HE IMMEDIATELY BLEW BOTH R MAIN TIRES. AS THE ACFT DECELERATED; CTL BECAME INCREASINGLY DIFFICULT. THE ACFT EVENTUALLY LEFT THE R SIDE OF THE RWY AT APPROX 3/4 RWY LENGTH. THERE WAS NO SIGNIFICANT DAMAGE OTHER THAN TO TIRES; BRAKES; R MAIN GEAR DOOR; AND LOWER SURFACE OF R WING. THIS SIT WAS CAUSED BY THE POOR BRIEFING ON HOW THIS CHK WAS TO BE ACCOMPLISHED BY THE PIC. THERE WAS ALSO AN ERROR IN JUDGEMENT WHEN THE PIC DECIDED TO START THE CHK ON A 6 MI FINAL. THIS PROC SHOULD ONLY BE DONE AT A SAFE ALT AND BE COMPLETELY FINISHED BEFORE APCH IS COMMENCED.