How to customize the resolution of CrunchBang in VirtualBox of Windows 7

Before you reading... here is a better solution to solve the problem of screen resolution:
How to install the Guest Additions for CrunchBang in VirtualBox of Windows 7

Host system: Windows 7 x64
Guest system: CrunchBang 11 ``Waldorf'' x64

I've just installed CrunchBang in VirtualBox two days ago, but the resolution was limited so it cannot fit my monitor properly. After some trials (including some struggles when installing the so-called Guest Additions), I successfully changed the resolution to my need.

I mainly followed the instruction of the link: How to adjust the screen resolution in Debian?

But there's some more work to do to make the change permanently. We need to add the following lines (from my own setting) in ``~/.config/openbox/autostart'':

xrandr --newmode "1920x1002"  159.50  1920 2040 2240 2560  1002 1005 1015 1040 -hsync +vsync
xrandr --addmode VBOX0 "1920x1002"
xrandr --output VBOX0 --mode "1920x1002"