Update VirtualBox to 4.1.8

• Download VirtualBox-4.1.8-75467-Win.exe
• Download VBoxGuestAdditions_4.1.8.iso
• Unmount the VBoxGuestAdditions.iso under "Parameters | Storage | IDE Controller"
• Do the update of VirtualBox
• Restart VirtualBox
• Copy the new VBoxGuestAdditions ISO into c:\program files\oracle\virtualbox
• Mount the new VBoxGuestAdditions ISO under "IDE Controller"
• Start the new VM
• Re-install VBoxLinuxAdditions like previously done:

sudo mount /dev/cdrom /media/cdrom
cd /media/cdrom
sudo ./VBoxLinuxAdditions.run
sudo reboot

• Unmount the VBoxGuestAdditions ISO

In case of problems with VirtualBox Guest Additions:
http://www.if-not-true-then-false.com/2010/install-virtualbox-guest-additions-on-fedora-centos-red-hat-rhel/