TURBOJET INBOUND TO MEV DSNDS BELOW ASSIGNED ALT WHILE TRYING TO PROGRAM FMS UNDER RNO APCH CTL.

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APCHING OUR DEST; MINDEN; NV (MEV) FROM THE S; WE WERE IN CONTACT WITH ZOA. WE REQUESTED DIRECT SPOOK INTXN FOR THE GPS-B APCH INTO MEV AND REQUEST WAS GRANTED. APPROX 3 MINS FROM SPOOK; ZOA SAID RENO APCH COULD NOT ACCEPT THAT APCH (SINCE IT IS PARTIALLY IN RENO'S AIRSPACE) BECAUSE OF CONFLICTING INBOUND TFC TO RENO. THEY THEN ASKED OUR INTENTIONS. WE REQUESTED DIRECT VIKES INTXN FOR THE GPS-A TO MINDEN. THEY CLRED US DIRECT TO VIKES AND TO 'DSND AND MAINTAIN 14000 FT' THEN TURNED US OVER TO RENO APCH WHO HAS JURISDICTION ON THE WHOLE GPS-A APCH AND HAD THIS COMPLETED WHEN WE WERE WITHIN 1 1/2 MINS OF VIKES. WE WERE STILL DSNDING AT THIS POINT TO 14000 FT. THEN; RENO INSTRUCTED US TO HOLD AT VIKES AS PUBLISHED. AT THIS POINT THE FO TRIED TO SELECT HOLD IN THE FMS; BUT WASN'T ABLE TO FOR 2 REASONS: 1) HE COULDN'T REMEMBER WHERE TO SCROLL TO GET THE HOLD FUNCTION; AND 2) WE WERE SO CLOSE TO VIKES THAT THE COURSE INDICATOR SLEWED TO THE NEXT COURSE FOR THE APCH. BECAUSE WE WERE OVER THE FIX ALREADY; WE TRIED TO GET A 'DIRECT TO' FUNCTION BACK TO VIKES SO WE COULD HOLD; BUT THE COURSE DEV INDICATOR KEPT SLEWING THE FMS AND THE 2 QUICK SUCCESSIVE CHANGES TO OUR CLRNC; I NEGLECTED TO PRESS 'ALT SELECT' FOR OUR 14000 FT CLRNC. RENO NOTIFIED US OF OUR ALTDEV AT THIS POINT. WE HAD DSNDED TO 13400 FT. WE IMMEDIATELY CLBED BACK TO 14000 FT. THIS EVENT WAS CAUSED BY A BREAKDOWN IN CREW COORD AND SOP'S BY BOTH OF US DIVERTING ATTN TO PROGRAMMING THE FMS AND CLRNCS THAT WERE ISSUED AT A TIME IN WHICH THE CREW WAS NOT READY TO ACCEPT THEM. WE SHOULD HAVE ASKED FOR DELAYING VECTORS IN ORDER TO PROGRAM THE FMS IN TIME AND TO KEEP OUR SOP'S AND CRM WORKING. AS A NOTE; SINCE THIS WAS NOT AN OVERLAY GPS APCH; THERE WAS NO WAY TO TAKE A STEP BACK IN AUTOMATION IN THE COCKPIT. WE HAD TO TOTALLY RELY ON THE GPS FUNCTION OF THE FMS.