As we mostly use RDMs with vmware I do this all the time. This should apply to a physical server as well.
1: Shutdown the server.
2: Take a snapshot of the volume contaning the LUN.
3: Resize the LUN to the desired size.
4: Boot the server on the gparted cd and expand the partition. Do not extend the drive to fill maximum space, if you do that you can have dodgy problems with windows detecting the new size but the filesystem will still be thew old size. Just leave a GB or so as free space just to be sure. ( http://gparted.sourceforge.net/download.php )
5: Boot normally on windows and enjoy the free space.
6. If something goes wrong just restore the LUN from snapshot.