Can{hundred-handed one} block each creature with his orginal power/thoughness?
No. {Hundred-Handed One} can only block 1 creature per combat (like normal) until its monstrosity ability has been activated.
he can block 100 when monstrous so just make sure they don't have 101+ :P
However he'll most likely die after one block with that power/toughness so making him indestructible or give him protection will work well :)
So yes while monstrous he can block 100 with his power/toughness but he'll die unless you save him somehow
119.2a Damage may be dealt as a result of combat. Each attacking and blocking creature deals combat damage equal to its power during the combat damage step.
He blocks up to 100 creatures once monstrous, but each attacking creature deals damage equal to their power to him.
119.5. Damage dealt to a creature or planeswalker doesn't destroy it. Likewise, the source of that damage doesn't destroy it. Rather, state-based actions may destroy a creature or planeswalker, or otherwise put it into its owner's graveyard, due to the results of the damage dealt to that permanent. See rule 704.
119.6. Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.12, "Regenerate") and during the cleanup step (see rule 514.2).
Those are a bit confusing, but they mean that if the total damage your creature is dealt by all the attacking creatures it's blocking adds up to more than it's toughness, it dies. It doesn't block each attacker with a different power/toughness. Make sense?
That's why {Guardian of the Gateless} is better :P
Or an indestructible {palisade giant}
Or {Abu Ja'far} with {Blaze of Glory}... Gotta kill em all!!!