FLC OF A CPR JET OVERSHOT ALT ON DSCNT ARR RESULTING IN ARTCC RADAR CTLR INTERVENTION IN ORDER TO AVOID A POSSIBLE CONFLICT WITH OTHER TFC 1000 FT BELOW. THE FO INADVERTENTLY HAD SET THE ALT SELECTOR TO 1000 FT BELOW ASSIGNED.

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WE WERE ENRTE FROM TYS TO GSO. THERE WERE NUMEROUS STRONG TSTMS ALONG THE RTE ASSOCIATED WITH A PASSING FRONTAL SYS. WE WERE CLRED TO TRAKS INTXN TO BEGIN OUR ARR INTO GSO. I WAS FLYING WITH A NEW COPLT WHO HAD FLOWN ONLY 4-5 PREVIOUS TRIPS ON THE AIRPLANE. ZTL (132.97) CLRED US TO DSND TO FL240; HOWEVER; THE COPLT ENTERED THE WRONG ALT IN THE ALT SELECTOR WHICH DIRECTED OUR DSCNT PATH TOWARDS FL230. AT APPROX FL235 ZTL QUESTIONED OUR ALT AND THE COPLT RESPONDED THAT WE WERE DSNDING TO FL230. CTR INSTRUCTED US TO CLB IMMEDIATELY TO FL240 AND ADVISED US OF TFC AT FL230 AND ITS LOCATION RELATIVE TO OURS. I EXECUTED AN IMMEDIATE CLB TO FL240. IT IS NORMAL OPERATING PROC FOR THE COPLT TO ENTER THE ALT IN THE ALT SELECTOR WHEN GIVEN AN ALT CHANGE BY ATC. HE THEN REPEATS THE ALT TO ATC; THEN REPEATS IT AGAIN TO THE CAPT. ON THIS OCCASION HE MADE A MISTAKE WHEN ENTERING THE ALT IN THE SELECTOR AND DUE TO EXISTING CONDITIONS (WX AND HIGH WORKLOAD) I WAS UNAWARE OF THE MISTAKE UNTIL WE WERE ADVISED BY CTR. AT THE TIME OF THE OCCURRENCE; I WAS DISPLAYING WX RADAR ON THE MFD. I BELIEVE THIS SIT MAY HAVE BEEN AVOIDED IF: 1) TCASII HAD BEEN DISPLAYED ALONG WITH WX RADAR. 2) COPLT HAD MORE EXPOSURE TO THIS ACFT. THERE WAS AN ADVISORY FROM THE TCASII AFTER WE HAD BEGUN THE CLB TO FL240. ACCORDING TO ZTL SUPVR; THE TFC WAS 3.8 NM AWAY AT FL230.