Personally, I don't see the point of such a debate. There is no common language here at all, and, accordingly, there will be no winning and losing, merely two compeltely different animals trying to re-arrange each other's DNA.
It may go something like this:
Moderator: Mr. Bush, where do you stand on the question of Israeli military activity in Lebanon?
Bush: I stand in support of the Israeli right to protect the soveriegnty of their nation, as I would stand for the support of any nation to do so, in the face of aggressive incursion. Although this conflict has been fraught with unfortunate military actions, on both sides, I do believe, in essence, that the Israelis did not start this process as the aggressors.
Moderator: Mr. Ahmadinejad?
Ahmadinejad: The Zionist conspiracy to subjugate the Muslim world must be stopped at any cost. To long have we stood idle as the dark forces of the Zionist regime walked the Earth among us. Allah be praised, we will stand against their fascist nation, side by side, muslim by muslim, and, Allah be praised, wipe every last one of them from the collective memory of our world. Allah be praised.
Moderator: How do you see this situation being peacefully resolved?
Bush: An enduring cease-fire, if held, can lead to negotiations and, eventually, given a less-subective international peace-keeping presence, some semblence of order can be maintained while we broach the subject of prisoner exchanges.
Ahmadinejad: Peace will be accomplished only when the Zionist plague is finally wiped clean from the sands of the middle east. Islam can and will prosper in the face of the Jewish cancer, and, god willing, will then be free to blanket the Earth unhindered and unimpeded. Death to the infidels! Allah be praised.
There may be variations, with certain sentiments hidden rather than overt, but this debate will prove nothing, demonstrate nothing and solve nothing. I hope that Bush rejects the offer because taking this guy on will only legitimize him well past the point of reasonability.