Store Drupal files outside of the root
On linux, you could create a symlink to the other folder, or mount it over NFS etc..

On Windows you can actually create a symlink as well.

Something like this should work:

# Open a windows terminal and
mklink /J "C:\Webroot\Drupal\Mysite\sites\default\files" "D:\Data\Drupal\Mysite\"


That should create a hard link connecting the files folder across the two drives, with the data being stored on D:

More info: 


http://en.wikipedia.org/wiki/NTFS_symbolic_link
http://en.wikipedia.org/wiki/NTFS_junction_point