OPERROR LTSS INVOLVING ACR X ON DEP AND GOV Y OPPOSITE DIRECTION APCH FOR AN ILS RWY 18. ACR X DEP RWY 36.

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I WAS PNF ON THIS LEG TO ORD. AFTER ENG START WE FOUND THERE WAS A DELAY FOR TKOF OF ABOUT 20 MINS AND WERE GIVEN TAXI INSTRUCTIONS TO RWY 36 WHERE WE COULD WAIT OUT THE DELAY. AS WE WERE WAITING OUR DEP TIME; GOV Y; A KING AIR; DEPARTED RWY 36 WITH A FLT CHK CALL SIGN. WHEN OUR TIME WAS UP WE WERE CLRED FOR TKOF TO MAINTAIN 5000 FT AND A L TURN TO 320 DEGS. WE ENTERED THE CLOUD DECK ABOUT 400 FT AND STARTED THE L TURN. TWR AGAIN INSTRUCTED THE L TURN AND CALLED TFC AS A FLT CHK ACFT INBOUND ON THE RWY 18 ILS. VERY SOON AFTER THAT CALL TWR CAME BACK WITH A TURN TO 220 DEGS AND THE TCASII CALLED OUT 'TFC.' WE INCREASED THE BANK ANGLE AS SOON AS WE HEARD THE 220 DEG HDG. BY NOW WE WERE OUT OF 1000 FT AND THE TCASII RA'S WERE ENABLED. TCASII INSTRUCTED A 'DSND; DSND.' TWR INSTRUCTED A 220 DEG HDG; AGAIN CALLED THE TFC; AND I THINK IT WAS HERE THAT HE SAID SOMETHING TO THE EFFECT OF 'HE TURNED RIGHT ON ME.' OUR DSCNT TRIGGERED THE GND PROX SYS. IT RESPONDED WITH A 'TERRAIN TERRAIN.' AS WE LEVELED OFF AND COULD SEE THE ACFT ON TCASII OFF TO THE R AND PASSING US; WE CONTINUED THE CLBOUT. THE ENTIRE INCIDENT WAS IN IMC. NUMEROUS FACTORS WERE INVOLVED WHICH CONTRIBUTED TO WHAT I FEEL WAS CTLR ERROR. TWR WAS WORKING GND AND TWR THAT MORNING AND THE FIELD WAS IFR. A FLOW TIME TO O'HARE CAME UP AT THE SAME TIME GOV Y WAS RUNNING A FLT CHK OF THE OPPOSITE ILS. TCASII WAS DIFFICULT TO READ BECAUSE THE INITIAL RANGE IS 20 NM. TKOF IS A BUSY TIME AND YOU MAY NOT BE THINKING FAST ENOUGH TO SELECT A CLOSE RANGE WHEN YOU'RE GETTING NUMEROUS INPUTS. I THINK THAT NEXT TIME I'LL PRE-SELECT A LOWER RANGE BEFORE TKOF FOR BETTER VIEWING. IT WOULD BE BETTER YET IF TCASII DEFAULTED INITIALLY TO THE LOWER RANGE.