The disk D: you referred to in the first post would be the Microsoft RAMDRIVE if you had booted using the Win98 boot disk floppy.
Usually you get a message saying that the diagnostic tools have been successfully to RAMDRIVE D:
This is a small area of your volatile memory (RAM) that has been assigned a drive letter by DOS to hold diagnostic tolls, etc. It is NOT a physical disk to be formatted or partitioned.
The fact that it is on drive D: indicates that there is a C: partition already created. If you had a disk with two partitions (C: & D
or had booted with CD-ROM support enabled, then the ramdrive would be assigned the next letter in sequence (E