A B733 CREW TAXIED PAST THE HOLD SHORT LINE DURING TAXI FOR TKOF.

Narrative

I WAS THE FO ON ORIGINATOR OUT OF MHT ON MAR/XA/01. I HAD COMPLETED MY WALKAROUND AND FOUND NOTHING UNUSUAL. A COUPLE OF MINS PRIOR TO PUSHBACK; THE 'A' FLT ATTENDANT CAME FORWARD AND TOLD THE CAPT AND ME THAT A PAX WHO WAS SEATED ON THE R SIDE NEAR THE #2 ENG WAS COMPLAINING ABOUT A 'COWL FLAP' OPEN ON THE R ENG. THE CAPT ASKED IF I HAD SEEN ANYTHING UNUSUAL DURING MY PREFLT; WHICH I HAD NOT; AND HE ASKED ME TO LOOK OUT MY SLIDING WINDOW TO SEE IF I SAW ANYTHING. I LOOKED AND STATED THAT NOTHING WAS AMISS. WE HAD COMPLETED THE BEFORE TKOF CHKLIST AND WE TAXIED OUT FOR DEP ON RWY 35 AT MHT. I HAD SWITCHED TO TWR AND WE WERE APCHING THE HOLD SHORT LINE FOR RWY 35. THE HOLD LINE IS IN AN UNUSUAL PLACE A WAYS BACK FROM THE RWY AND I HAD FLOWN INTO MHT SEVERAL TIMES BEFORE AND KNEW THE CAPT HAD ALSO. I SHOULD HAVE ASKED IF HE KNEW WHERE THE HOLD LINE WAS BECAUSE AS WE APCHED THE HOLD SHORT LINE; THE 'A' FLT ATTENDANT CAME BACK UP FRONT AND BEGAN TALKING ABOUT THE 'COWL FLAP' AGAIN. RIGHT THEN BOTH THE CAPT AND I BECAME DISTR AND WE ENDED UP LETTING THE NOSE AND NOSEWHEEL ROLL PAST THE HOLD LINE WITHOUT A TKOF OR POS AND HOLD CLRNC. I TOLD THE TWR. I BELIEVE THAT THIS COULD HAVE BEEN AVOIDED IF I HAD NOT LET MYSELF BECOME INVOLVED IN THE DISCUSSION AS THE AIRPLANE WAS UNDER PWR. ALSO; I SHOULD HAVE ASKED THE CAPT IF HE WAS FAMILIAR WITH THE HOLD LINE. I COULD HAVE ALSO RAN BACK OUTSIDE PRIOR TO PUSH AND CHKED THE ENG AGAIN. WE BOTH WERE THINKING TOO MUCH ABOUT THE CUSTOMER VERSUS TAXIING.