How have your docs ended up on C drive? Did you move the documents folder to C:. I don't know if this is possible but suspect not.
If you have been logging onto the remote desktop and saving docs in the administrators "Documents" on C:, you could create another share, via the dashboard on D: and move those files to D:.
Normally C: is 60Gb and only contains the OS. Not near my WHS at present but the OS, with a few extra addins, is around 30GB if I remember correctly.
The remainder of the first HD becomes D: which is where the documents folder resides by default along with other shares.
Dave
The Frog on the Lilypad at Home