How do I 'Push Off' an object?

I'm trying to make a fighting game, but I cannot figure out a way to push the player off the top of the enemy's head when he lands on it. I need to be able to push the player to the left or right depending on where the player lands on the enemy's head. Here's a quick example of what I want to achieve.

<img src="https://dl.dropbox.com/u/13338856/Untitled.gif">

Is this more or less what you want ? Download.

It's one way of doing it

Dude that's perfect! I never thought it would be so simple!

Thanks You could tweak some things like vertical push etc.