A B737-700 FLT CREW INADVERTENTLY FORGET TO TURN BACK ON THE PACKS AFTER TKOF AND INITIALLY MISINTERPRETED THE ALT WARNING HORN AS HAVING AN ACFT CONFIGURATION PROB. THE RPTR STATES THAT THE DUAL USE WARNING HORN CONTRIBUTED TO THE DELAYED RECOGNITION AND THE DEPLOYMENT OF THE O2 MASKS.

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OUR FLT DEPARTED AT XA10 WITH A NORMAL NOISE ABATEMENT TKOF PROC USED (TOGW 127500 LBS WITH MAX PWR; FLAPS 5 DEGS; CUTBACK; ETC). A NO ENG BLEED PROC WAS USED FOR THIS DEP. THE AFTER TKOF CHKLIST WAS INITIATED AT 6000 FT; DUE TO THE EXTENDED CLB PHASE FOR NOISE ABATEMENT. WE WERE STEPPED CLBED TO 10000 FT; DIRECT ZZZ1; THEN 14000 FT; 16000 FT; AND FINALLY FL260. PASSING APPROX FL230; THE CABIN ALT WARNING HORN SOUNDED. BEFORE WE COULD REACT TO THE HORN; THE MASTER CAUTION; OVERHEAD AND PAX OXYGEN ON LIGHTS ILLUMINATED. REALIZING OUR MISTAKE; THE ENG BLEEDS WERE IMMEDIATELY TURNED BACK ON AND THE CABIN PRESSURIZED IN 'AUTO.' THE DEPRESSURIZATION CHKLIST WAS REVIEWED AND THE CAPT PLACED THE PRESSURIZATION SYS INTO 'MANUAL' MODE. THIS PRESSURIZED THE CABIN FASTER AND AFTER A CABIN ALT OF LESS THAN 10000 FT; I PLACED THE CONTROLLER BACK TO 'AUTO.' THE CAPT WENT ON THE PA SYS TO COMMUNICATE WITH THE PAX AND INTERCOM SYS TO COORDINATE WITH THE REST OF THE FLT CREW. I CONTINUED TO MONITOR ATC AND THE AUTOPLT. THE CAPT ASKED FOR A LOWER ALT; BUT WAS DENIED DUE TO TFC. WE ASSESSED THE SIT AND NOTED THAT THE ACFT WAS PRESSURIZED AND THROUGH CREW COORD; WE HAD ENOUGH OXYGEN TO CONTINUE TO DEST. ACCORDING TO THE LEAD FLT ATTENDANT; UPON DSCNT; SOME PAX WERE ACTIVATING THEIR OXYGEN 'JUST TO TRY IT.' OUR FLT ARRIVED WITH AN UNEVENTFUL LNDG AT XB13. LOOKING BACK; THE PROB STARTED WITH NOT RECONFIGURING THE ENG BLEEDS DURING THE AFTER TKOF CHKLIST. THIS CAN BE ATTRIBUTED TO A COUPLE OF THINGS: 1) THIS PARTICULAR PROC WAS AROUND 1 MONTH OLD TO OUR COMPANY AND NOT ALL CREWS WERE USING IT. 2) IT WAS A RATHER BUSY NIGHT OVER THE TERMINAL AREA AND ALONG WITH A DEP RPT; MY RADIO CALLS WERE SOMEWHAT CONTINUOUS. ANOTHER CONTRIBUTING FACTOR IS THAT THE CABIN ALT WARNING HORN WAS MISIDENTED AS THE CONFIGN WARNING HORN. THIS MAY BE DUE TO THE FACT THAT ALL OF OUR RAPID DECOMPRESSION TRAINING IN THE SIMULATOR IS DONE IN THE CRUISE PHASE OF FLT. ALSO OF IMPORTANCE IS THE SIMILARITY BTWN BOTH WARNING HORNS. THE ERROR CHAIN; ONCE REALIZED; WAS QUICKLY BROKEN WHEN COORD AND TRAINING CAME INTO PLAY. THE ABILITY TO STAY FOCUSED AND NOT TO LOOK BACK AT THE 'WE SHOULD'VE' AND 'WE COULD'VE' PLAYED A MAJOR ROLE. IF ANY MEMBER OF OUR CREW GOT FIXATED ON THE MISTAKE; THUS CONTINUING THE ERROR CHAIN; THE INCIDENT MAY HAVE TURNED OUT A LOT WORSE.