I have a scene in my short film where the camera pans horizontally across a field, and I have a PSD sky that I want to put over the sky in the footage.
I originally tried to do this entirely on PS, applying the sky layer manually onto every frame (600 frames total) and shifting it a couple pixels each time to correspond with the panning. I am unhappy with the result, and figured there must be a better way of doing it.
For this purpose I have just purchased AE CS4 and am entirely new to it. If somebody could give me an easy-to-understand explanation of how to do this shot, it would be a true life saver.
First of all, I strongly recommend that you work your way through the getting-started materials here before you attempt to work on a real project.
This After Effects Community Help search pulls up several resources for sky replacement. This page is probably the best of those results to use as a starting point, since it links directly to several good tutorials on the subject.