Fading in and out in MX

Well I am basically half way home, but I can’t quite figure out how to make my movieclip gradually fade out. What I want is an arrow to appear and dissappear when the user is around some buttons. Here is my code:

stop();
speed = 5;
_root.onEnterFrame = function() {
greenArrow._x += (_xmouse-greenArrow._x)/speed;
if (_xmouse > 0 && _xmouse < 340 && _ymouse > 0 && _ymouse < 60) {
greenArrow._alpha += 10;
} else {
greenArrow._alpha = 0;
}
};

I’ve tried just creating an if else and then changing the operators to the exact opposite, but no dice.

Any help out there? Thanks in advance…