I'm new to this king of logic. I want to create an object (Mc) that can move
alone inside a defined area. Like a bug in my screen. This is to create a small
game.

Any idea or tutorial or...
Tanx in advanced

Humm
When it comes near of a border it can change direction. I want to learn how to
program some king of movement. I know there is Math.sin, Math.cos and other but
how to use it?

It's a general question. Nothing specific. Just want to learn more in this
king of programmation. It's different of building an application. It's like
Artificial Intelligence.

you'll need to initiate a loop. setInterval() is an easy way to do that.
you'll need to define your bug's speed and initial direction of travel. here's
an example of a bug moving within (roughly) a rectangle:

speed = 5;
dir = Math.PI-2*Math.random()*Math.PI;
moveI = setInterval(moveF, 80);
function moveF() {
if (bugMC._x+speed*Math.cos(dir)+bugMC._width>400) {
dir = (2*Math.round(Math.random())-1)*Math.PI/2+Math.random()*Math.PI/2;
}
if (bugMC._x+speed*Math.cos(dir)<200) {
dir = -Math.PI/2+Math.random()*Math.PI;
}
if (bugMC._y+speed*Math.sin(dir)+bugMC._height>400) {
dir = -Math.random()*Math.PI;
}
if (bugMC._y+speed*Math.sin(dir)<200) {
dir = Math.random()*Math.PI;
}
bugMC._x += speed*Math.cos(dir);
bugMC._y += speed*Math.sin(dir);
bugMC._rotation = 180*dir/Math.PI;
}

Thats cool. It's something like that I want. Is there some tutorial or code
that makes an object (MC) following a curved line (guide). The clip follows
this line, when it arrived at the final point, a new line is create as a guide
for the clip. In that way the clip could move smoothly.

if you can define your curve (with parameters, for example), you can use
actionscript to move your bug. however, if you cannot define the curve you
must use a motion guide.

i'm not sure what you mean, by "...that way the clip could move smoothly."

in what way does the code i suggested fail to do what you want?

Your code works great. I found something like what i'd like to be able to do.
Check that link :
http://www.macromedia.com/devnet/mx/flash/sample_files/html/amoebas.html

It's something like that but I would like that the small bugs (Mc) follow a
curved line. Actually they go straight to the point and then they change
direction.