On Windows Vista or later, the whole %appdata%\Bitcoin directory can be replaced with a symbolic directory link:
(0) Make sure the bitcoin client is not running.
(1) Move the %appdata%\Bitcoin directory to its target location (e.g. d:\bitcoinData)
(2) Run the command prompt as root and issue the command
mklink /d "c:\users\\appdata\roaming\bitcoin" "d:\bitcoinData"done!
This allows you to keep bitcoin client data anywhere, e.g. on a secure local fileserver.
EDIT::You should update your client to 5.2, there is no benefit in using the outdated version. Great many bugs were fixed since 4.0.
If you are using and older version of Windows with NTFS then I can send you an "ln" executable (or the source code for it in c++) that I whipped up years ago (just calls the API function to make a hard link - note that being a hard link the other logical drive must be on the same physical hard drive)...
Had you tried that yourself you'd know that bitcoin client crashes when using hard-linked directories.Try your own tool or grab Sysinternals Junction
from Microsoft and for crying out loud test your advice before posting.