Originally Posted by Boci
Not really, you can just attack from the side.
Originally Posted by The SRD
Movement During a Charge:
You must move before your attack, not after. You must move at least 10 feet (2 squares) and may move up to double your speed directly toward the designated opponent.
You must have a clear path toward the opponent, and nothing can hinder your movement (such as difficult terrain or obstacles). Here's what it means to have a clear path. First, you must move to the closest space from which you can attack the opponent. (If this space is occupied or otherwise blocked, you can't charge.) Second, if any line from your starting space to the ending space passes through a square that blocks movement, slows movement, or contains a creature (even an ally), you can't charge. (Helpless creatures don't stop a charge.)
So, no, you can't attack from the side. (By which I assume you mean "charge off to the side", because "from the side" makes no sense in a system without facing and wouldn't help with the geometry problem in any case.)
In further mounted combat nonsense: The mount, again, is the one making the charge. The rider just gets the opportunity to attack at the end of the charge, and derives charge benefits from it if he takes that opportunity. There's nothing intrinsically wrong with that, but it means that you can't do the classic lance charge against a Medium opponent while mounted on a standard warhorse. See, the charge doesn't end until the horse makes its attack (and the horse must
attack - it's the one making the charge). Warhorses have 5' reach. Lances have 10' reach, and don't threaten at 5'. At the end of the charge, when the rider gets the opportunity to make his attack, he doesn't threaten the target.