FLT CLRED DIRECT TO OBSCURE INTXN THAT HAD TO BE PROGRAMMED IN INS. WHEN PROGRAMMED; CAPT FLYING TURNED WRONG DIRECTION TO GO DIRECT; MISREADING THE INS COURSE INDICATOR.

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AFTER A NORMAL KENNEDY 5 DEP AND WHILE CLBING TO 13000 FT; DEP CLRED US INS DIRECT TO GREKE INTXN. SINCE THIS WAS NOT PART OF THE COMPANY PROVIDED FLT PLAN RTE; I WAS REQUIRED TO INSERT THE LATITUDE/LONGITUDE INTO THE INS AFTER THE CLRNC WAS RECEIVED FROM DEP. DURING THIS PROCESS ATC REQUESTED WE TURN TO HDG 010 UNTIL ABLE TO GO DIRECT GREKE. APPARENTLY THE CAPT HEARD MAINTAIN HDG 010 ONLY. AT THIS TIME I WAS INQUIRING AS TO THE CAPT'S UNDERSTANDING OF THE CLRNC AND HE WAS LEVELING AT 13000. ATC THEN CLRED US TO 14000 AND INQUIRED OF OUR HDG; RESTATED THE DIRECT CLRNC. THE INTXN WAS OVER 40 DEGS L OF OUR COURSE BUT THE CAPT STARTED A 30 DEG BANK TO THE R. BY THE TIME I WAS ABLE TO PROVE TO THE CAPT THE TRUE LOCATION OF THE CLRED INTXN ATC WAS REACTING STRONGLY TO THE ACFT'S WRONG TURN. I QUICKLY ASKED FOR A HDG TO THE INTXN AS WE NOTICED THE ACFT WAS AT 14200 FT AND STILL CLBING. ATC SAID MAINTAIN 14000. OUR TOTAL DEV FROM ASSIGNED ALT WAS 285 FT HIGH. LOOKING BACK; A FEW EVENTS SNOWBALLED INTO A BIG PROBLEM. HOWEVER; THE BIGGEST PROBLEM WAS REQUIRING THE USE OF INS IN OR NEAR THE TERMINAL AIRSPACE WHERE QUICK REACTION TO A CLRNC IS NECESSARY. AFTER ALL; OLDER ACFT SUCH AS THIS ONE; HAVE OUTDATED DISPLAYS WITH NO GRAPHIC DEPICTION OF INS COURSE AND LACK DATABASE FOR FAST SELECTION OF WAYPOINTS. IF ATC MUST USE RNAV IN CONGESTED AIRSPACE IT WOULD BE NICE IF THEY WERE REQUIRED TO PREFACE THE CLRNC WITH EXPECT DIRECT XYZ 30-60 SECONDS PRIOR TO ISSUING THE CLRNC OR BE REQUIRED TO ISSUE A HDG; DIRECT XYZ WHEN ABLE. AFTER ALL; DOES THE FOLLOWING MEAN YOU ARE R OF COURSE OR NEED TO TURN R TO GET ON COURSE -- R0001 R040? TO ME IT MEANS 40 DEGS R OF TARGET COURSE BUT TO MY CAPT IT MEANT TURN R 40 DEGS. UNFORTUNATELY; I WAS UNABLE TO PROVE I WAS RIGHT FAST ENOUGH!