If you haven't already, the first thing to do id install the VBox Guest Additions, doing so will give you a few more options for controlling the screen size from the VirtualBox machine menu.
It's likely that your installation will not be configured for compiling kernel modules, so trying to install the Guest additions may fail without some initial preparation. Before doing that, try installing the Guest additions:
- Select 'Install Guest Additions… from the Devices menu
- If the CD is not mounted automatically, run mount /media/cdrom
- Run sh /media/cdrom/VBoxLinuxAdditions-x86.run (replace -x86 with -amd64 if 64 bit)
If you receive an error message related to kernel headers you will need to carry out some additional steps:
- Open a root console
- Update your APT database with apt-get update
- Install the latest security updates with apt-get upgrade
- Install required packages with apt-get install build-essential module-assistant
- Configure your system for building kernel modules by running m-a prepare
This may take a while depending on the speed of your Internet connection. Once the above has completed, try running through 1 to 3 again.
If, once you have completed the above you find you still cannot resize the VBox window correctly, you may have to edit /etc/X11/xorg.conf