CAPT OF AN ATR72 OVERSHOT ASSIGNED ALT DURING DSCNT.

Narrative

DURING A DSCNT INTO VPS; ATC ASSIGNED OUR ACFT TO DSND TO 6000 FT MSL. DURING THE DSCNT OUR ADVISORY DATA UNIT FAILED. PER THE POH; THE FLT DIRECTOR AND AUTOPLT WERE TURNED OFF. ALSO DURING THE DSCNT THE CAPT AND I WERE DISCUSSING 2 THINGS: 1) THE USE OF RWY 30 AT VPS SINCE ATIS RPTED WINDS OF 310 DEGS AT 9 KTS; YET RPTED RWYS 12 AND 19 WERE IN USE. 2) ALSO DISCUSSED WAS THE CAPT'S STRATEGY FOR AVOIDING SEVERAL TSTM CELLS BTWN US AND THE VPS ARPT. DURING THESE DISCUSSIONS THE ACFT DSNDED TO APPROX 5600 FT MSL. JUST AS I CAUGHT THE ALTDEV; PNS APCH ASKED FOR OUR ALT. I QUICKLY RESPONDED TO ATC THAT WE WERE CLBING TO 6000 FT. THE CAPT QUICKLY CLBED BACK TO 6000 FT. UPON REACHING 6000 FT; I ASKED IF THERE WERE ANY CONFLICTS WITH OTHER ACFT DUE TO OUR ALTDEVS. THE CTLR RESPONDED BY SAYING; 'I GUESS NOT; IF WE WERE NOT SHUT DOWN.' EARLIER IN OUR DSCNT; ZJX ADVISED US THAT WE WOULD BE DSNDING OVER AN ACTIVE MOA THAT EXTENDED FROM THE SURFACE TO 5000 FT MSL. THE REMAINDER OF THE FLT WAS UNEVENTFUL AND THE VPS TWR GRANTED US THE USE OF RWY 30 AFTER WE REQUESTED THE USE OF RWY 30 ON OUR INITIAL CONTACT WITH THE VPS TWR.