A B737-200 FLC CLBS OUT OF ITS ASSIGNED ALT OF 10000 FT DURING AN AUTOPLT DISCONNECT BY CAPT WHEN ACFT SPD ACTIVATES THE SPD WARNING SYS SW OF IAD; VA.

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MY LEG (CAPT). BRAND NEW FO (FIRST LINE TRIP!). WHILE LEVEL AT 10000 FT MSL; RECEIVED 'URGENT' ACARS MESSAGE TO CALL COMPANY. THEY WANTED TO KNOW WHY WE PUSHED 1 MIN LATE! FO DIDN'T KNOW HOW TO USE ACARS YET; SO I RESPONDED WHILE FLYING ON AUTOPLT. THE AUTOTHROTTLES DISENGAGED FOR SOME REASON (FAULTY PERFORMANCE DATA COMPUTER SYS WE FOUND LATER) AND WHILE I WAS ENGAGED WITH THE ACARS; THE ACFT ACCELERATED TO 350 KTS. I NOTICED THIS JUST BEFORE WE GOT THE HIGH SPD CLACKER AND IMMEDIATELY RETARDED THE AUTOTHRUST AND AUTOPLT. ACFT MOMENTARILY 'ZOOMED' TO 10800 FT. WE WERE THEN CLRED BY CTR TO FL210. SUPPLEMENTAL INFO FROM ACN 456319: AFTER LEVELING AT 10000 FT; THE ACFT CONTINUED TO ACCELERATE TO THE BARBER POLE SPD AND THE CLACKER SOUNDED. THE CAPT DISENGAGED THE AUTOPLT AND PULLED BACK THE THRUST LEVERS. THE PLANE STARTED THE CLB. I CALLED 'ALT' AT ABOUT 10300 FT. WE PROBABLY REACHED 11000 FT BEFORE STARTING A DSCNT BACK TO THE ASSIGNED ALT. ON THE WAY BACK DOWN; ATC CLRED US TO A HIGHER ALT. (I SUSPECT THAT THE CTLR NOTICED THE DEV; BUT DIDN'T MENTION IT). I BELIEVE THAT THE OVERSPD WAS CAUSED BY A PERFORMANCE DATA COMPUTER MALFUNCTION; A FAILURE TO REDUCE FROM A CLB TO A CRUISE THRUST SETTING WHEN WE LEVELED AT 10000 FT. THE CLB MAY HAVE BEEN A RESULT OF THE CAPT PULLING BACK ON THE YOKE; OR A TENDENCY OF THE ACFT TO PITCH UP WITH FULL THRUST APPLIED WHEN THE AUTOPLT WAS DISENGAGED. I WAS REVIEWING ENRTE CHARTS. NEITHER OF US NOTICED THAT THE THRUST LEVERS DID NOT COME BACK AS THEY SHOULD HAVE WHEN REACHING TARGET CRUISE SPD. TO PREVENT RECURRENCE; BOTH CREW MEMBERS SHOULD MORE CLOSELY MONITOR THE PERFORMANCE OF THE AUTOPLT.