ACR LGT WAS FORCED TO GIVE WAY SLIGHTLY TO A COMMUTER ACFT TO MAINTAIN COMFORTABLE SEPARATION DURING PARALLEL VISUAL APCH TO DEN.

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WHILE ON A VISUAL APCH TO RWY 26R IN DEN; AT ABOUT 5 MI OUT ON FINAL; WE WERE ADVISED THAT A COMMUTER AIRPLANE WAS ON A RIGHT BASE TO RWY 25. AT THE TIME THE WX WAS CAVU; BUT WE WERE UNABLE TO PICK OUT THE TFC INITIALLY. WHEN WE DID FINALLY SEE HIM THE ACFT WAS TURNING ONTO THE FINAL APCH JUST AHEAD AND TO THE RIGHT OF US. I WOULD ESTIMATE THAT HE WAS SLIGHTLY LEFT OF THE CENTERLINE OF RWY 25. LAT SEP APPEARED TO BE 300' OR LESS; AND THE ACFT APPEARED TO BE DRIFTING TOWARD THE CENTERLINE OF RWY 26R; WHICH PUT HIM IN CLOSE PROX TO US. I WAS FORCED TO EVADE TO THE LEFT TO KEEP SOME SEMBLANCE OF SEP; AND BY THIS TIME WE WERE ABOUT 1 MI FROM THE RWY. A SIGNIFICANT FACTOR IN THIS INCIDENT WAS THAT I WAS UNABLE TO GET A WORD IN WITH THE TWR TO CONFIRM THAT THE COMMUTER ACFT WAS IN FACT GOING TO LAND ON RWY 25; AND NOT 26R. BOTH ACFT LANDED W/O INCIDENT. I SPOKE TO THE TWR SUPVR ON DUTY AT THE TIME AND HE AGREED THAT IT WAS A BAD POLICY; BUT THEY WERE FORCED INTO IT BECAUSE OF THE HEAVY TFC LOAD AND OF THE SPD DIFFERENCES BTWN THE DIFFERENT TYPES OF ACFT; THEY WERE UNABLE TO PROPERLY STAGGER THE APCHS. I BELIEVE THAT THIS IS A DANGEROUS SITUATION AND SHOULD BE CORRECTED.