Once rebooted, Ubuntu should boot up with better video support. Unfortunately, VirtualBox 2.2.0 Guest Additions does not correctly install Mouse Integration for Ubuntu 9.04. To fix this select Applications -> Accessories -> Terminal, and type sudo nano /etc/X11/xorg.conf. press the Page Down key to scroll down the file. At the bottom, copy and paste (paste into the terminal using Shift + Control + V) the following:
Press Control X to save then type sudo reboot to restart the VM one final time. This should now enable Mouse Integration. it safe to enable 3D Acceleration after this.
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