Nikon D300 Complete Manual page 746

If we have to change the dpi value (but not change the
original pixels), we do this by:
1. Unchecking the Resample Image box in
Photoshop's Image Size dialog.
2. Entering a new value in the Resolution box in the
Image Size dialog. (For an Epson and most other
inkjet printers, I'd suggest 288 pixels/inch.)
If you then need to resize the image, set your dpi value as just
described, then
3. Recheck the Resample Image box.
4. Enter new dimensions in the Width and/or Height
boxes. However, if you perform this step, you'll no
longer be dealing with the actual pixels you captured
while shooting, but Photoshop's interpolation of them
at the new size.
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 746