The CNC milled head and the extra heavy-duty gusset on the down tube (see photo). The geometry is also slightly tweeked, but only a lttle bit. Enough to accomadate an 80mm (KK) or 100mm (Score) fork. The weight difference is about 200 grams depending on the size. My 17" Score weighs in at just over 1800 grams and my 18" KK just over 1600. The main difference is intended usage; the Score being an "out of bounds" bike, which is Kona's classification for a freeride bike. However the OB hardtails are not meant for hucking and huge drops, but slower technical courses with jumps and obstacles. The Score was replaced by the Shred and Scrap DJ bikes in 2001, though they were still classified as OB at the time. I've seen plenty of kids riding these in the North shore, so they can definitely take it. The Score also came with disc tabs. So there are a few differences. The tech I wrote with at Kona still considers the Score an OB bike, and said it might best be compared to the Hoss if it were to be compared to a more recent bike (as opposed to Stuff, Scrap, Shred or the new Caldera.) Hope that wasn't too confusing, but Kona can get confusing sometimes.
I see you have the 17" KK I want
I've looked at that pic a few times. VERY nice ride you have there! Stevek said that they started putting disc tabs on the KK near the end of production in 2000. Mine doesn't have them, but apparently there are some out there. 2000 was also the last year of production, not including the new line from this year.