You should have the message below :

Sun VirtualBox Headless Interface 3.1.4
(C) 2008-2010 Sun Microsystems, Inc.
All rights reserved.

-s, -startvm, –startvm <name|uuid>   Start given VM (required argument)
-v, -vrdp, –vrdp on|off|config       Enable (default) or disable the VRDP
server or don’t change the setting
-p, -vrdpport, –vrdpport <ports>     Comma-separated list of ports the VRDP
server can bind to. Use a dash between
two port numbers to specify a range
-a, -vrdpaddress, –vrdpaddress <ip>  Interface IP the VRDP will bind to
-c, -capture, –capture               Record the VM screen output to a file
-w, –width                           Frame width when recording
-h, –height                          Frame height when recording
-r, –bitrate                         Recording bit rate when recording
-f, –filename                        File name when recording.  The codec
used will be chosen based on the
file extension