I am creating a slide show rear projected on a 6 foot wide by 8 foot high screen. I have about 50 images. I want to display these images on a grid pattern with approximate 48 spaces (each space about 1x1). I want to be able to add and subtract images from this pattern. This means at any one time i could have one image or 20; 5 images beside each other or 5 scattered over the grid.
Another layer of complexity would be to shift from say 30, images of x pixels, to just two images which fill the horizontal dimensions of the screen.
Can anyone point me toward a methodology/software for this project?
Well, needless to say, I think that laying out the smallest possible grid, either with guides or placeholder files would be the way to start. I would also strongly suggest that you do this in After Effects, which would make it much easier.
In AE, I would use a script such as Advanced Composition Grids, or Motion Boutique's free script, Collage:
Collage would give you the option to setup your initial layout from placeholder layers, and then randomly generate ideas for additional layouts. On AE Scripts site, there's also Gridder, and Layers2Grid, which might help out. If you have a solid visual concept in your head, you may not want the ability to brainstorm, using the tools above, so my main suggestion would be to create a bunch of comps within a single project, one for the 48 space grid, one for the 3 images, one for the 5 images, etc., using placeholder layers, which you can then replace with your final images. You could also do this in Photoshop, but I think that After Effects would give you the most flexibility.