[F8] tap 2 buttons back and forth

Hey, I’m interested in creating a game where you tap 2 buttons alternating for example the left and right arrow keys that in turn makes a meter go up. Kind of like those old nintendo track and field games where you’d hit a and b back and forth as fast as possible to make the character go faster. In this case you’d be hitting them back and forth to raise a meter with the goal of getting it as high as you can.

Here is an example (http://www.gamedesign.jp/flash/sprinter/sprinter.html) of a game that does this.

I think this tutorial (http://www.kirupa.com/developer/actionscript/multiple_key_detection.htm) is on the right track. It detects multiple key combinations except you have to hold the first key down and then press the second; where as, I would like to be able to tap the first key and then tap the second to make something happen.

Any help?

Thanks,
Jason