Oh it is a trivial topic, but will requires guest additions to work and I just wanted to double check this :
VirtualBox 4.1.10 r76836 win.amd64 (Mar 14 2012 18:18:53) release log
00:00:08.514 Guest Additions information report: Version 4.2.6 r82870 '4.2.6'
1. you're using a mismatch version between your guest additions and your Virtualbox installation.
2. Your Virtualbox installation is still 4.1.x, which is quite old now and I am not sure it actually supports what you want. Have you tried with the latest Virtualbox version?