Actionscript to create movement rather tha tweens?

I’d be very interested to see how this motion is achieved with actionscript alone and not with tweening. This is the scenario I would like to see - two buttons that dont move of course

When button one is pressed a green square slides in nice and smoothly using actionscript. When button two is pressed, the green square slides out and is replaced with a blue square - so whenever on of the buttons is pressed, the square on screen slides out before the other one slides in.

It would also be good if the green square and blue squares were in their own swf files and loaded into levels rather than an empty movie clip.

Could this be done?

Thank you
I use mx - not mx2004