Yes certainly you can have the RealTracks and/or bb folder on the D: drive.
Do you have an existing bb/RealTracks folder on your D: drive? How large is it and how much free space do you have on that drive?
Yes.
I have d:\Music\BIAB\RealTracks\ 34.1G
and
d:\Music\BIAB\Drums\ 4.8 G
Free space on d: is currently 98 G.