It's cute, really -- a couple of small bits of trig well placed, and you get a nice lazy Susan.

Start here: http://softsurfer.com/Archive/algorithm_0104/algorithm_0104B.htm

If you are looking for a long and good article on how to use Vectors for games:

http://www.tonypa.pri.ee/vectors/tut06.html

(Its in flash, but so what?)

When I was working on the XAct.Win.Controls.GraphRenderer I had to work with Vectors to emulate hit testing on NET CE.

Since I'm back in to needing vectors for work I'm doing on the acceleration of the Carousel, I went and looked up what I wrote...

In case this is of use for anyone else (wish it were a bit more documented).

The object's velocity is its existing V, plus the effect of A, over a time interval

V2 = V1 + (a * t);

Given a control of 300x300, containing a circle (of r=150):

Again, pretty simple (until you need it 'yesterday'):

double angle = Math.Atan2((p2.Y - p1.Y), (p2.X - P1.X));

This should not need saying: