Projection matrix from two points

[Jeff McWhirter <jeffmc@xxxxxxxxxxxxxxxx>]

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?

Thanks,
Jeff