Scrolling a timeline movie

hi, i am working on my school website, and i am working on the timeline of my school history, but i got stuck…

this is what i wrote;

ActionScript:--------------------------------------------------------------------------------onClipEvent (load) {
_x = 0;
_y = 0;
div = 5;
}
onClipEvent (enterFrame) {
_x += (endX-_x)/div;
_root.context.plus_one.onRelease = function() {
if (_x>=-400) {
endX = _x-100;
}
};
_root.context.plus_two.onRelease = function() {
if (_x>=-300) {
endX = _x-200;
}
};
_root.context.plus_three.onRelease = function() {
if (_x>=-200) {
endX = _x-300;
}
};
_root.context.minus_one.onRelease = function() {
if (_x<=400) {
endX = _x+100;
}
};
_root.context.minus_two.onRelease = function() {
if (_x<=300) {
endX = _x+200;
}
};
_root.context.minus_three.onRelease = function() {
if (_x<=200) {
endX = _x+300;
}
};
}


the problem is when i click the button again when it is scrolling, the order would mess up…

here is the swf:
http://hk.geocities.com/aroom2003/timeline_beta.swf

please help me…