|"2.73 gbson system sav(d)"|
That makes me think that the 'D' partition is not empty, but is the 'image' that is used to restore your system when it becomes corrupted. I would strongly suggest that you do not use it to expand your C: drive.
That is unless you still have the option to create recovery CDs from it. Doing that would depend on the PCs manufacturer.
The best advice would probably be to clone the drive to a new larger drive, and replace the current one.