Sorry to revive an old thread, but I have a solution to this issue where I have written a script that does all that you want:
1) without requiring hstart and the command prompt window does disappear.
2) It launches the VM as a seamless/headless/maximised
3) Even if you did somehow manage to close the terminal/cmd window it WILL NOT pull the plug on your virtual machine!
4) If you look at the script it not only allows for that safety factor but it actually starts it in a fresh new process and closes the CMD window for you anyway, this way you leave the virtual machine open and running in its own process
5) It IDs the Virtual machine via its ID number and not its name and location so Virtualbox automatically knows what virtual machine you wish to launch without needing to know its path location in reference to the script location

[code]@echo off
if not "%minimized%"=="" goto :minimized
set minimized=true
start /min cmd /C "%~dpnx0"
goto :EOF
:minimized
rem Anything after here will run in a minimized window
rem bring the current directoty forward and change drives cause windows normally starts your process from system32
rem bringing the process forward to the script location means it will launch myscript from its location
%~d0
CD %~dp0
cls
rem Open the folder in a new process and close/exit this one
start /wait /b C:\PROGRA~1\Oracle\VirtualBox\VirtualBox.exe --startvm "6de1a76e-ee30-4844-b578-a2453026c14e" /SEPARATE/N
exit[/code]

Note that code is for my own Virtualbox Ubuntu ID, put yours in there. If you like
Basically plonk this on your desktop or in your startup folder and create a user called Ubuntu in Windows 7 and use the same credentials in Win7 as Ubuntu. Set the screen in Win7 never to lock or require password to unlock. Set boot into Ubuntu to auto-log in but have password prompt on screen awake resume! DONE

Anyway, as far as I can tell, it looks like MS changed the way it implemented SMTP AUTH in Outlook 2007. This change has been carried over into Outlook 2010. Outlook 2010 tries to encode credentials with MD5 or better. When I query BT’s servers, this is what I see:

[root]# telnet mail.btconnect.com 25
Trying 213.123.26.152...
Connected to mail.btconnect.com.
Escape character is '^]'.
220 mail.btconnect.com ESMTP
ehlo eel.co.uk
250-mail.btconnect.com Hello eel.co.uk
250-8BITMIME
250-SIZE 52428800
250-ETRN
250-DSN
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN PLAIN
250 PIPELINING


The mail server is only offering LOGIN or PLAIN and Outlook apparently isn’t prepared to stoop so low. Furthermore, from what I’ve read, DIGEST-MD5 authentication was broken in Outlook 2007 in any case and remains so in Outlook 2010.

Most solutions out there depend on using POP before SMTP for implicit authentication but since our POP and SMTP servers are physically separate (provided by different organisations in fact), this is not an option for us. Ironically the “fix” would appear to be to downgrade to Windows Live Mail (or Thunderbird), but given the size of our I.T. estate, that would be a mammoth project.

I’m still waiting for a proper fix in Outlook, but since no one seems to understand the SMTP RFCs any more, I’m not going to be holding my breath. We just have to live with the fact that the leading email client (for better or worse) has introduced incompatibilities with legacy systems.

Bah!