Voldemort would have had to commit murder on the grounds at Hogwarts in order to turn it into a Horcrux. My reading of the story suggests the soul has to be split and embedded into the object at the exact time of the murder. Have we had any suggestion that he killed somebody when he arrived?

My guess is that he wanted Gryffindor's sword.

Er... could we have a recap of the Horcruxes so far? I'm a little rusty; only read HBP once...
-Riddle's diary (destroyed)
-the ring (destroyed)
-the locket (with RAB)
-Hufflepuff's goblet

What were the other two? Dumbledore speculated Nagini, which I don't buy. Was there something of Ravenclaw's that was mentioned?