The horned helmet (Races of Faerûn 155, 156) (25 gp; 4 lbs.) is a martial Small weapon (hence light in dnd-3.5e terms) with which a Medium creature deals 1d4/×2 points of piercing damage. Already, I am amused (but not surprised) that the Gruumsh Martial Weapons College has as a required course Introduction to Helmets 100: Goring for Pleasure and Treasure, but it gets better: The weapon's description says
A horned helmet resembles a normal helmet with bull’s horns attached to each side. A horned helmet deals double normal damage when used during a charge action, but the helmet has a reach of 0 ft. (156)
What does a Medium creature's turn look like if the creature that's wielding (on its head, presumably) a horned helmet charges 30 ft. across a featureless plain at, for example, a hill giant? By the same token, what does such a creature's turn look like if the creature wants to make a full attack using its horned helmet against an adjacent hill giant?
Note: I assume the creature must enter the foe's space, but how the creature can do that and what happens to the creature afterward are significant concerns (square occupancy in particular). And, yes, of course this Medium creature intends to wear an inappropriately big horned helmet so that the creature can benefit from wielding the horned helmet two-handed while using the feat Power Attack. See, too, in Races of Faerûn the spiked helmet, an identical weapon dealing slightly less damage for
weirdos folks who don't use antlers in all of their decorating. While Races is for dnd-3e I plan to use this in a dnd-3.5e campaign, hence tags for both; however, answers should focus on the weapon's use in the latter game.