Try the current DNG converter to convert the file and open in Photoshop versions older than CS5, though I don't know how far back the compatibility goes. Getting a newer version of Photoshop is part of the "upgrade tax" we all pay when we get bigger, better, faster and larger cameras/files.
Simply working on either camera-generated jpeg or tiff files leaves not much to be desired.
As I tell people, I shoot all my files as raw files since I don't like what Mr. Nikon working in a cubicle somewhere in Tokyo has decided to throw away before I see all that my camera can offer me. Jpeg files throw way easily 95% of the information before writing a file. I want all that my camera can give me!
Camera-generated tiff files are a little better quality wise, but few can tell the difference between a properly-crafted tiff or jpeg from the camera. Still, half the image data is gone at the push of a button and then you get files much larger than raw with the color quality of a jpeg that takes forever to download and crams your media cards with but a few files. Not a good thing IMO.
