As written, yes.
A Medium character can wield Large weapons, but their relative encumbrance category is increased by one step, and he takes a -2 penalty.
Powerful Build allows a half-giant to wield Large weapons without penalty. The only penalty given is the -2. If he wields a Large longsword, he can do it with two hands; it's still a two-handed weapon for a Medium creature. If he attempts to wield a Large greatsword, he can't; it's larger than a two-handed weapon.
Monkey Grip allows a Medium creature to wield Large weapons without increasing their relative encumbrance category, but he takes a -2 penalty in so doing.
A Half-Giant with Powerful Build as written and Monkey Grip could wield a Large longsword in one hand (MG) at no penalty (PB), or a Large greatsword in two hands (MG) at no penalty (PB).
A Huge weapon is not affected by either ability - both refer specifically to weapons designed for creatures one size larger.
Now, as noted, it seems that what they wrote for Powerful Build is probably not what they meant to write... but what they meant to write is unclear once you start talking about Huge weapons.
-Hyp.