Hey man,
that's a classic with Flash 5
ActionScript Code:
if (this._y<=380) {
this._y += 10;
}
if (this._X>=530 and this._y>=18) {
this._y -=10;
}
When your clip has reached the bottom right position, this.y<=380 si false, and this._X>=530 and this._y>=18 is true, so you move up.
Next, both this.y<=380 and this._X>=530 and this._y>=18 are true, so you tell your movie to go up by 10 and down by 10.
You can solve that by using another variable (a boolean) to know whether you're going up or down, and another for the left/right motion.
pom