So I recently set up a VirtualBox VM on my Windows 7 machine so I could access my XFS hard disk through a network share.
Being there's no way to hide a VirualBox VM by default (even by running in headless mode), I went ahead & wrote a quick C# program to hide running windows.
First of all, I created a .bat file to run my VM headless...the contents are as follows:
cd "C:\Program Files\Sun\VirtualBox"
VBoxHeadless.exe -s Ubuntu
Here's my error-prone, crappy window hiding app:
If it crashes your system, doesn't work, etc.......too bad! :)