Find the graph of equation...

Hi, I'm having trouble figuring out the answer to this question:

Find an equation whose graph consists of all points P(x,y) whose distance from the point F(0,p) is equal to its distance PQ (there should be a line above the PQ) from the horizontal line y = -p (p is a fixed positive number).

This is my effort of reproducing the graph that came with it:

http://img.photobucket.com/albums/v6...2/untitled.jpg

I thought I could do it by plugging (x,y) and (0,p) into the standard equation of a circle, but I'm not getting the same answer as is listed in the book (they say that it's x^2=4py (parabola))

Any help greatly appreciated!