And how exactly it didn't work? Let's assume you have a window with two buttons, "Start game with character A" (startA) and "Start game with character B" (startB).
Then the script attached to the window would contain the following event handlers:
...
on "startA"
{
Game.LoadActor3D("path\charA.act3d");
Game.ChangeScene("path\some.scene");
}
on "startB"
{
Game.LoadActor3D("path\charB.act3d");
Game.ChangeScene("path\some.scene");
}