Problem with enemy bullets

I have a small problem and I was hoping that someone can help me.
I have this vertical space shooter and I have problem regarding enemy bullet directions.
My problem is this.
When enemy ship shoot bullet at me(player) I want this bullet to be aimed to my current location, and to continue to travel to that location and beyond, even if I move to another location…Im sure you know what I mean, but my English is bad and this is best I can do to explain.
I tryed to do this on my own with players location as waypoint and bullet cheking his x and y locations against players and then navigating bullet acordingly but it didnt helped.Im almoust certain that some kind of Math method is necessery but i just cant figure it on my own.
I would apricciate if someone could help me.
Thanks in advance.