Finding a point relative to a center point?

I’m having a hard time phrasing this question properly, so I apologize in advance if I sound like a moron.

I’m trying to figure out how to find a point relative to the center of an object, modified by its rotation. For example, in the attached swf, I’ve been messing around trying to draw trails to a bitmap, coming out of the thrusters. I didn’t have a problem at first, but as the ship rotated, the lines that were being drawn wouldn’t remain relative.

http://donkling.com/SpaceShips.html

I’m sure this is because I have no idea what I’m doing, and I’ve just been sort of idioting my way through it. That aside, is there an easy way to find the point I’m looking for? For instance, say I want a point at Y -14 of my ship, but I want that to remain relative to the ship as it rotates. Am I making any sense whatsoever? Thanks in advance for any advice.