Hard Trance is sort of sweeping, generally with bigger breakdowns and buildups. Similiar in construct to regular trance, but faster, harder, and alot better in my opinion! Hard house is not without its breakdowns and buildups, but nowhere near as sweeping as Hard Trance. Also tends to have that tougher sound to it with hoovers etc (not saying HT doesnt have hoovers, though). I also find that generally HH tunes are shorter in duration than hard trance.
There are tunes that kinda make the line between the two rather hazy.