MISINTERPRETING INFO ON AN UNFAMILIAR GPS SYSTEM; A BEECHCRAFT PLT DSNDS EARLY ON PRACTICE IFR APCH.

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I WAS ON APCH AND LOST POSITION AWARENESS DUE TO SEVERAL FACTORS. THE CONDITIONS WERE VFR SO I COULD SEE AND AVOID OBSTRUCTIONS OR OTHER ACFT; AND NONE WERE INVOLVED. I DID HOWEVER GET LOW ON THE APCH. CONTRIBUTING FACTORS WERE A NEW GPS WAS BEING USED TO MONITOR THE APCH AND ALTHOUGH I HAD USED IT BEFORE (JUST FOR VFR FLT) -- THIS WAS THE FIRST TIME I USED IT ON AN APCH. IT GAVE ME THE DISTANCE TO THE NEXT FIX. I HAD PROGRAMMED IT TO GIVE DISTANCE TO ARPT; BUT IN THE APCH MODE IT GIVES DISTANCE TO NEXT FIX; SO THIS CONFUSED ME. I THOUGHT I WAS CLOSER TO THE ARPT THAN I ACTUALLY WAS. I ALSO HAD A GLIDESCOPE FAILURE AT THE SAME TIME (IN THE ACFT) BUT FAILED TO NOTICE THE FLAG UNTIL I HAD GONE LOW ON THE APCH. THE CTLR THANKFULLY WAS WATCHING ME AND ADVISED ME I WAS LOW AT THE FAF --- NOT PAST THE FAF AS I THOUGHT. I WAS TRYING TO DO TOO MUCH USING A NEW PIECE OF EQUIP WITHOUT DOING MORE PRACTICE WITH IT IN A PRACTICE ENVIRONMENT. I ASSUMED A HIGHER WORKLOAD THAT I SHOULD HAVE WITHOUT ADDITIONAL COCKPIT RESOURCES AVAILABLE. NEXT TIME I GET A NEW PIECE OF EQUIP I WILL USE IT IN THE VFR PRACTICE ENVIRONMENT PRIOR TO TRYING IT IN IFR AND NOT LET NEW EQUIP INCREASE MY WORKLOAD -- INSTEAD I WILL USE IT TO DECREASE MY WORKLOAD.