If you're still using '98se on the desktop, re-boot to a DOS prompt and type the command;
D: (D and a colon) [Enter]
does it change to your D: drive?
If so, you could use DOS to copy the required files to space on your C: drive. At least that will rescue the files.
It's a puzzle why Windows has failed to recognise your D: drive. Have you checked it is physically working? Only last week, I had a machine that could not see a drive, and the power cable had become detached!