In regards to Photoshop 4, if you could recommend one feature for me as a beginner to concentrate on, that was pretty basic, but enhanced photos tremendously, what would it be?
Speaking for myself, I achieve the best results lightening underexposed/shadowed areas with:
Enhance -> Adjust Lighting -> Lighten Shadows
This is an editing feature of Photoshop Elements 5.0. I assume something like it exists with Photoshop 4.
Another feature I use lot is cropping to a 3:2 format (for 4 x 6 prints) from the 4:3 format that is used with most cameras sold today. But this can be done with the uploading tools of Kodak and most photo processing labs.