Hi there!

As Northcode points out, you have to use Application.quitApplication. There's pretty much no difference between AS2 and AS3, so something like this:

Code:
import com.hippohx.Application;

myButton.onPress = Delegate.create(this,buttonHandler);

function buttonHandler(){
   Application.getInstance().quitApplication();
}
There are AS2 samples, but are old and no longer maintained, you can find them here:

http://code.google.com/p/hippohx/sou.../hippohx/demo/

If you have any more problems just join the mailing list:

http://groups.google.com/group/hippohx

It's been a coincidence that I've come across this post : )

Hope this helps!

Juan