EMB145 CREW DSNDED BELOW CLRED ALT UNTIL THE GPWS ACTIVATED.

Narrative

DURING VECTOR FOR ILS APCH; VOR AND ILS EQUIP WERE BEING USED AS PRIMARY FLT INSTS AND FMS WAS BEING USED AS BACKUP DISPLAYED ON THE MULTI-FUNCTION DISPLAY. THE CAPT (MYSELF) WAS FLYING THE ACFT. DURING INITIAL CONTACT I THOUGHT THE CTLR SAID TO EXPECT THE ILS TO RWY 28L. THE FO HEARD TO EXPECT RWY 28R CORRECTLY. WE EACH PROGRAMMED OUR FMS EQUIP ACCORDINGLY. WHEN I DISCOVERED WE WERE GOING TO RWY 28R; I ASKED THE FO TO SET MY FMS TO THE PROPER APCH AND I SET MY VHF RADIOS TO THE PROPER FREQ. WE WERE DSNDING TO 3000 FT AT THE TIME. WE WERE GIVEN FURTHER DSCNT TO 2500 FT; BUT THE ALT PRESELECT WAS NOT SET PROPERLY AND WE DSNDED TO 2000 FT; AT WHICH TIME OUR ACFT GPWS TOLD US WE WERE TOO LOW; GEAR NOT DOWN; 1000 FT AGL. I ASKED ATC WHAT ALT I SHOULD BE AT. HE CLBED US TO 3000 FT AND WE FINISHED THE APCH WITHOUT INCIDENT. THIS PROB I THINK WAS DUE TO SPENDING TIME PROGRAMMING THE FMS; WHICH WAS NOT NEEDED TO START WITH; AND NOT FOLLOWING PROPER PROCS FOR SETTING THE ALT PRESELECT AND CONFIRMING BTWN THE 2 PLTS.