Is there anything important on D that you might want to save?
If not, I'd advise you to format the D disk. Then it's completly clean.
If you still have stuff on D, or programs, don't format the disk.
Unless you don't care about whiping the disk clean.
Open the dir of This Computer. Then rightclick the D-disk, select Format.
Quick format will just tell the disk to overwrite all files and ignore excisting files if there are any.
Full Format will completly whipe the disk clean, even the folders.
Quick format should do the trick if you want it clean.
Full Format is only if you are planning to sell your disk to unknown people.
Because Quick Formatted disks can still be recovered.
I hope I helped you.