Chris Hecker's dynamics tutorials also a good start.

I've got some code that's derived from his equations, but no docs.

Ignore the collision detection part. Everything physics related is in the Body class. The response code uses a few things.

mtd : that's the amount of intersection between bodies.
tcoll : time of collision (I'm doing swept tests).
ncoll : normal of collision;
contact : the two contact points on the two bodies.

What the response does is
1) separate intersecting bodies (using the mtd).
2) generate a collision impulse (so they bounce).
3) generate a friction impulse (so it's more fun).

a body has a few properties :
position : 2D cartesian vector representing position of the centre of mass in space
velocity : 2D cartesian vector representing the linear velocity of the body.
orientation : angle of the body (just one float is needed in 2D).
angular velocity : how much it spins.
inverse mass : the inverse of the mass of the body (if body is unperturbed by collisions, invmass = 0).
inverse inertia : the inverse of the angular inertia of the body (if body doesn't spin after collisions, invinertia = 0).

what inertia is for rotations is like what mass is for linear movement. The higher the inertia, the more difficult it is to rotate. The higher the mass, the more difficult it is to push around.

I use the inverse of mass and inertia, so coding inert bodies is easier (set properties to 0, that plugs straight into the equations with no fussing about).

There is a sticky thread on physics engines and reference material in this forum. You'll find numerous references there. As a starting point, I highly recommend the Essential Math tutorials, linked in that thread and available for download as powerpoint files. These are the presentations from a 2 day tutorial given at the Game Developer's Conference each year in San Francisco, prepared by industry professionals with a lot of practical experience on making physics fast and robust. You will learn from this a lot of the basic problems and a bit of math. It's a good starting point. There are other references in the sticky thread that cover the math in significant more detail, in addition to other replies to your query here.

I would start with implementing circle-circle collision detection and response, and then using that as a base for more complicated dynamics. Searching for pool/billiard physics should turn up a bunch of easy to read code.