MLG ON APCH MAKES A GAR DUE ACFT ON END OF RWY.

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I WAS THE SIC AND PERFORMING THE PNF DUTIES OF A SCHEDULED ACR (B-737) FLYING AN INST APCH TO RWY 23L IN NIGHT RESTR VISIBILITY CONDITIONS. DURING OUR COMS SWITCH OVER TO THE TWR; WE WERE CLRED TO LAND AND ADVISED THAT THERE WAS TFC XING OUR RWY AND THAT THE TFC WOULD BE CLR UPON OUR ARR. WE SAW AN ACFT EXITING OUR RWY DOWNFIELD AND BELIEVED THAT ALL WAS WELL AS WE CONTINUED OUR FINAL DSCNT. AT ABOUT 150 AGL; THE CAPT SUDDENLY NOTICED THAT AN MD-80 ACFT WAS SITTING RIGHT ON OUR RWY; 90 DEGS OFF; AS IF HE WERE XING THE APCH END OF THE RWY. WELL; HE WAS STOPPED THERE; SO WE EXECUTED A GAR AND MADE AN UNEVENTFUL RETURN TO LAND SAFELY. WHAT WENT WRONG? US -- THE MESSAGE THAT TFC WAS XING OUR RWY WAS SPECIFIC. THE TWR CTLR DID SAY THE 'APCH END' BUT BOTH THE CAPT AND I MISSED THE INTENT OF THE WORDS BECAUSE WE SAW ANOTHER ACFT EXITING THE RWY AND MADE AN ASSUMPTION. OTHERWISE; OUR GAR WOULD HAVE OCCURRED EARLIER BECAUSE WE WOULD HAVE BEEN LOOKING FOR THE OTHER GUY. HIM -- HE WAS LOST AND IN A SPOT NOT ASSIGNED TO HIM. TWR HAD CLRED HIM TO CROSS RWY 23L AND POS HIMSELF ON RWY 23R. HE MUST HAVE BECOME CONFUSED AND DECIDED TO DO NOTHING UNTIL HE GOT HIS BEARINGS. MEANWHILE; HERE WE CAME -- RIGHT AT HIM. HIM -- NO AIRPLANE ILLUMINATION AS HE SAT SIDEWAYS ACROSS OUR RWY. HAD HE TURNED ON A LIGHT OR 2; PERHAPS WE WOULD HAVE SEEN HIM A LOT SOONER. TWR -- LOST THEIR AWARENESS OF THE SIT AND DID NOT TAKE CTL TO ENSURE THAT FOLKS WERE DOING AS THEY WERE TOLD. I'M NOT SURE THAT THEY WERE ABLE TO SEE THE ACFT ON THE GND EITHER. ALL OF US -- COM. WHEN THE PLT OF THE ACFT ON THE GND BECAME CONFUSED; HE NEEDED TO COMMUNICATE RIGHT NOW (REMEMBER CONFESS) IN ORDER TO ALLOW OTHERS TO HELP AND/OR REACT. WE SHOULD HAVE PAID CLOSER ATTN TO THE XING LOCATION SPECIFIED BY TWR AND TWR NEEDED TO STAY ON TOP OF THE SIT. GND MOVEMENT OF ACFT NEAR ACTIVE RWYS HAVE PROVEN TO BE QUITE DANGEROUS IN LOW VISIBILITY SITS IN RECENT YRS.