B757-200 CREW TRIED TO FLY A VNAV APCH FOR RWY 30L AT SJC. THEY HAD AN ALT OVERSHOOT WHEN THEY WENT TO FLCH.

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VNAV VERSUS FLT LEVEL CHANGE. CLRED FOR VOR DME RWY 30L APCH AFTER VECTORS. STARTED DSCNT ON VNAV AND INTENDED TO TRY AND FLY APCH ON VNAV. QUICKLY DISCERNED THAT VNAV WOULD NOT MAKE THE 16.8 DME AT 4300 FT FROM 8000 FT SO DEPLOYED SPD BRAKES. BOTTOM ALT OF 1700 FT WAS IN MCP WINDOW FOR VNAV PROCS. SELECTED FLT LEVEL CHANGE TO GET DOWN AND WAS DISTRACTED OR CONCENTRATING ON DSCNT AND WENT THROUGH THE 4300 FT 16.8 DME LEVELOFF POINT. VFR FLT CONDITIONS AT THE TIME AND RWY/ARPT IN SIGHT SO ASKED FO TO REQUEST VFR APCH TO SJC RWY 30R. ATC CLRED US FOR VFR APCH AND NO COMMENT ON MISSED ALT AT DSCNT POINT; NO TFC CONFLICTS. AUTOPLT TURNED OFF AND HAND FLEW TO LNDG ON ALTS. GENERALLY UNDER VFR CONDITIONS AND ILS APCHS TO SJC ATC WILL OFFER VFR APCHS. BUT WITH RWY 30L CLOSED AND THE SIDESTEP MANEUVER IN PLACE WITH THE PAPI IN PLACE THE APCH PARAMETERS SET YOU UP TO FLY A SIMULATOR TYPE OF PROFILE TO MINIMUMS WHICH IN VFR ISN'T NECESSARILY PRUDENT. IT IS DIFFICULT TO PICK UP THE PAPI/VASI FROM THE FAR DISTANCE AND TO GO TO MINIMUMS ON ALL ALTS IN VFR SORT OF CHALLENGING AT BEST AND ESPECIALLY DISCONCERTING TO SKIM THE SAN JOSE SKYSCRAPER TOPS ON FINAL AT 700 FT. THE ERROR ON MISSING THE ALT WAS MY FAULT FOR NOT USING SIMILAR TYPE NON-PRECISION PROFILE PROCS; WHICH I BRIEFED BUT AT THE LAST MIN TRIED THE VNAV METHOD. SHOULD HAVE STAYED WITH BOOK PROC ON SETTING THE NEXT ALT; ETC.