Hi Tom,
What I usually do is scan the photo at 600 dpi and then reduce it to 300 dpi in photoshop, then sharpen it adjust the tones to match the print as closely as possible, then I will reduce it again to my final res, usually about 100 dpi (I like to leave a little extra just in case). Use unsharp mask, and adjust the sliders until the image is sharp enough, but not too sharp, and save as a jpeg/high quality.
Hope that helps.