Transitions between movieclips in a container

My buttons are inside movieclips. Each button attaches another movieclip from the library into a container. Everytime I try the swf by pressing any button, it attaches perfectly to the container. The problem is that once a movieclip is attached, if I press another button, the new movieclip does not substitute the previous one.

Furthermore, I am also trying to have a nice transition between movieclips as per this tutorial:

http://www.kirupa.com/developer/mx2004/transitions.htm

The only difference is that this tutorial is for external swf and in my example, all the movieclips are already in the library.

Please help me. Here is the actions I have for the on release state:

on (release) {
if (_root.currMovie == undefined) {
_root.currMovie = “contact”;
_root.container.attachMovie(“contact”, “contact”, 1);
} else if (_root.currMovie != “contact”)
{
if (_root.container._currentframe >=
_root.container.midframe) {
_root.currMovie = “contact”;
_root.container.play();

}
}
}