3.5nd dnd – Planetary collision vs combat zone of a large opponent

So I have this situation: Largo the Great, who is Great, charges Count Countercharge, who has prepared his feat, and is of average height.

The question is: does Largo, RAW, get a zone effect on the account?

The reasons I would not think are:

1) I seem to remember that you can not take an AoO, but I can not find where I am from.

2) Is an AoO during a charge possible? I do not think – again, I can not find why.