Windows7 hardlink over two different drives
Solution 1:
A hard link is a file system feature that cannot cross a file system boundary. You can't hard link files on C: to D: because they are separate file systems. They might each contain the same type of file sytem (eg. NTFS) but they are separate file systems.
Solution 2:
If it's Windows 7, you can use symlinks - Steam Mover does just that.