samba vs windows
From my experience with windows, the only tools you have for doing this sort of thing are are Map Network Drive and SUBST. Neither are exact enough to do what you wish. If you cannot house everything from the existing D: on the RHEL box then you are snookered. If you can then you copy all the data across, then reassign the physical drive letter in Windows device mangler (Control Panel, System, hardware), and map the samba share to D:.
Hope that helps.