I have successfully installed existing ubuntu 10.10 on win7 host http://kirilligum.wordpress.com/2011/02/17/run-existing-linux-ubuntu-10-10-partition-in-virtualbox-under-host-windows-7-system-on-thinkpad-x201t/ . everything worked
I did a clean install od win7 and ubuntu. then i tried to follow the same steps and install existing ubuntu 11.04 in win7's VB. it didn't work well. VB does not grab the mouse. it also gives an error after grub "error: hd0 out of disk" and asks to press any key. after the error it boots into login screen but as i said it doesn't grab the mouse. i tried installing vb guest additions. it didn't help either. i also couldn't find xorg.conf file in /etc/x11 on ubuntu 11.04
has anyone had success with this?