Projection matrix from two points

We're playing around with flythroughs in the IDV and I am trying to figure
out (I am particularly brain dead trying to think in 3D) how to
create a projection matrix from two points, (x1,y1,z1) (x2,y2,z2)
such that the camera position is at the first point and the point of view
is towards the second point.

Any ideas?