Flash professional CS 5.5 actionscript 2.0 platform game help, can't jump over rock

Sorry, need some help again!

I have took a video of the problem
[URL=“http://www.youtube.com/watch?v=Hye39hn4KgE”]http://www.youtube.com/watch?v=Hye39hn4KgE

[COLOR=#000000]
[/COLOR]I want to make my character jump over an object and also jump onto higher platforms
I drew a rock, made it into MC, and gave it a script

onClipEvent (enterFrame){
if(_root.miku.hitTest(this)){
_root.miku._x-=10;
}

}

this stops my char from going through the rock but when i jump over, it resets back my position somewhere else, and i can still go through the rock from the top, i set a platform on top of the rock and put a barrier script

onClipEvent (enterFrame){
if(_root.miku.hitTest(this)){
_root.miku._y-=10;
}
}

it doesn’t help much, and my char is now floating

question is : how do i set it to jump over the rock smoothly instead of it reseting my position
and how do i make my char jump to a higher platform and make her stay there (i think it has something to do with gravity)

sorry i m getting all the key terms mixed up, like barriers, collision detect, gravity etc…

but yea, my objective is : to make like a mario style game, able to jump on higher platforms, and jump over objects. that’s for the basic. thank you all and merry christmas!

=)=)

ArCh~
Cheers